Troubleshooting Internet Explorer 7
Many of us, when we install a beta and immediately encounter problems, will blame the beta we have installed and uninstall it (sometimes complaining very vocally about how bad quality control is.. and how MS were such idiots to release something that is obviously broken), but it may not always be that simple.
Here is a basic truth. Microsoft is not going to release a build of Internet Explorer 7 that is fundamentally broken. They...just...won't... do... it. Remember that basic truth and you have a fighting chance of working out what is wrong.
Troubleshooting problems
The first thing to do is READ THE RELEASE NOTES. There are known issues and you may save yourself hours of grief if you make sure you are informed before you install.
If your particular problem is not discussed in the Release Notes, the most important thing you can do, when encountering problems with IE7, is to run IE in no add-ons mode.
Some weird and wonderful problems have been "fixed" by running IE7 in no add-ons mode. If no add-ons mode fixes your problems, then you are going to have to try and work out what third party product is causing your problems by disabling one add-on at a time, restarting IE, then testing. If disabling one doesn't work, re-enable it, restart IE, and try the next one. Once you work out what is wrong, feel free to post a comment here and share what you have learned.. you will do good 
As a side note, Internet Explorer follows certain rules when it comes to add-ons. If the add-ons are in use at the time IE7 is installed they will automatically be enabled. It is only new add-ons (active x) that are disabled until you give them permission to run. You may have an old control that is broken in the latest version of IE.
So, what do we do if disabling Add-Ons doesn't help? Well, that all depends on what the problem is, so let's go some basic stuff that is known to be the most common causes of breakage.
1. Adjust the size of your cache and delete your History and Cookies
Traditionally Internet Explorer has set the size of its temporary internet files folder to a percentage of total disk space. In recent years, with the massive increases in hard drive capacity, this has led to the cache being set to ridiculously large sizes... far too large for IE to be able to cope reliably. Web sites may slow down, pictures may stop displaying, hyperlinks may stop working (actually, they haven't stopped working, its just that IE is collapsing under the weight of all that saved data), you may see the classic "page cannot be displayed" error... and that's just for starters.
Click on IE, Tools, Internet Options, General Tab, Settings
Set your IE cache to between 50 and 250 Meg (I recommend 50)
Next, delete all temporary internet files, including offline content (IE tools, Internet Options, General tab, Delete button). Delete your IE history and all cookies. Then, restart IE.
2. Third party software interference
This is not the same as disabling add-ons. Shut down all other programmes, not including your firewall, to see if things improve (don't forget about the icons in the system tray). Antivirus and antispyware products that are set to scan internet data can cause problems. Your firewall may be set to block pictures.. your antivirus or anti-spyware scanner may be removing data or disabling features to protect you from the bad guys.
Spybot and other programs, for example, may stop you from changing your home page. Some firewalls may block advertisements (and other graphics) so that you only see a red x, or block scripting. Some will block access to sites according to keywords.
Example: Just last week I was tasked with fixing a PC that was unable to access any Web site. "Page cannot be displayed" was all that we saw, no matter what site we checked.. yet at the same time Messenger was working, Outlook Express was working, I was able to Telnet to sites, Ping worked as did Tracert. Under such circumstances you'd assume that Internet Explorer was broken, yes? After all, everything else Internet related was working. Nope! It wasn't IE.
The clue was that it was only programmes that used Port 80 that were broken (including the antivirus programme, which used Port 80 for updates.
On this occasion a previous technican had installed, and then tried to remove, ZoneAlarm, but something had gone wrong. The True Vector service was still in services.msc, and set to Automatic, but could not be set to disabled (access denied) or removed from the registry (permissions error). In addition there was a "network monitoring device" in Hardware Device Manager. It took some careful work with a very special third party tool to delete the True Vector service registry entry despite the broken security permissions, and disable the "network monitoring device" via Device Manager, to "fix" Internet Explorer.
Second example: I've been working with Nick of softeq.com to try and resolve a problem with his banking site... the login button isn't working. Its an interesting problem. Running IE is no add-ons mode fixes the problem therefore that tells me, right there, that IE itself is not the problem. If we disable a TrendMicro add-in (for a Trend product that has been uninstalled) then the log-in button works (the add-in is WinNTCheck.dll and is related to the Trend Micro Client/Server Agent for SMB). But, the "fix" was not dependable. IE would suddenly fail again.
If we enable SSL 2.0 and "Allow pop up block to show input prompts" the site also starts working. But, it is important to note that I have always disabled "Allow pop up block to show input prompts" on my machines and the site works for me - Nick may not know this yet, but he and I use the same Bank, therefore if there was a problem with their sites (remembering I have been running IE7 since Alpha, when I was given a build that *nearly* killed my laptop's OS while I was travelling - I gave myself one heck of a fright) then I would know about it. Something else is wrong.
The basic fact that running IE in no add-ins mode fixes the problem points to a problem with a third party product, not IE per se. Sure, you can uninstall to get functionality back, but what good does that do? The problem may recur in the final version of IE7 if we don't report on, and try to fix, such problems.
3. Try spoofing IE6
Many sites have taken to serving different CSS styles to suit the Web browser that is visiting the site. Reality is that IE has done a real bad job in the past when it comes to CSS, and it is inevitable, when MS suddenly starts getting things right, that a lot of sites are suddenly going to break.
If changing the UAS (User Agent String) does not help your problem, please report the site in the newsgroups and to MS using the standard feedback options. Also, please send feedback to the site's owners so that they will be aware that they have to update their sites.
4. Malware
Yes, malware. Viruses, spyware, foistware, malware. There is stuff that may have been undetectable when it was installed. The real bad guys use cutting edge code to try and infect you. There is no antivirus or antispyware product on this planet that can protect us from everything. There will always be a window of opportunity between a virus/explioit being used, and detection being added to various protective softwares. This is why you *must* rescan on a daily basis, even if previous scans were clean and you have not been on the internet since.
4. Try a different Web browser
If an alternative browser works, at least we can rule out a basic problem with your internet connection.
I understand that by focusing on third party software and sites as being "at fault" I am going to frustrate some people, but the reality is that it is not possible for IE to be coded to suit the myriad internet related software programs out there and all the different ways of doing things. If MS codes to suit one programme, another *WILL* break. So, do what you can to track down what may be causing your problem and report it to the programme's owners. Encourage 'best practice' (as far as it is possible to quantify 'best practice').
We have a choice. We can maintain the status quo, and let sites coded to suit the old, broken, IE remain, or we can take the pain of all those broken sites, and use it to work to put the past behind us and update sites to suit the new IE7 that tries to be complaint as much as is possible.
Make no mistake - IE6 and earlier was broken when it comes to CSS - many sites put a lot of effort into working around those breakages and yes, site authors are going to be real peeved that their sites are suddenly broken.. but, hey guys, the fact that the IE team is trying to address problems, even if it breaks your hacks, is a *good thing*. Recode your sites to acknowledge what has been fixed. If you refuse, what reason do we have to continue improving?