This came up in a newsgroup posting the other day so I thought I would expand on my answer. The actual question was why there was not a link back to the portal home page on MySite in MOSS and how to add one?
To answer the first part of the question, you need to understand that the underlying architecture of SharePoint Portal Server has changed from 2003 to 2007. With the addition of Shared Service Providers you can now have many different top level SharePoint Portals all use the same MySite. This is a huge improvement over 2003 (at least in my opinion) especially if you come from a large company that is made up of many smaller companies. Each smaller company can have its own portal with its own look and feel and share the same MySite area.
The second part of the question, how to add the links, can be answered in at least three ways. All three involve the "My Links" menu bar that you can see at the top of your MySite page (actually it shows up wherever you are but since we are talking about MySite it is a good place to look ) . Think of this as your Internet Explorer Favorites for MOSS.
If you open this menu option you will see the first way to add the link; the "Add to My Links" menu option. This will allow you to enter your own link into the list. Just enter a link to whereever your home page is and give it a descriptive title, determine who can see these links (determines who can see if on the public side of your MySite), and enter a group (think of it as a Favorite's folder) where it will reside.
The second way involves the new concept of "Membership". If you belong to a site as a "Member", that site will (eventually) show in your MyLinks automatically. A small caveat to this is that you MUST be added directly as a "Member", not as a member of a group that is a "Member" for this to work. This is not a bug (I checked with MS) but rather it is working as designed. If you think about it, it does make sense. There would have to be a lot of checking going on to see if you belong to any of the groups that are "Member" of in all the sites. Maybe in the next version an efficient algorithm can be created for this but for the time being this is the way it will work.
The third way involves having a real nice SharePoint administrator add the link for everyone automatically. This is done under the Shared Services Administration page in the Central Administration site. Click the "Personalization Links" link and add the link to the home page. The nice thing about doing it this way is that A) it only has to be done once for everyone and B) you can target this link to audiences so if you are part of a large company made up of smaller companies you can set everyone's link correctly.