Over the weekend I switched my main machine to Windows 2008 and started playing with Hyper-V. I updated the RAM and threw in another hard-drive (man that stuff is so cheap at present !). I've got both Vista and Windows 2008 (different drives) on the machine, and even though Windows 2008 and Vista are the same kernel, Windows 2008 feels noticeably faster.. plus it has hyper-V. (note: Vista 32 bit, 2008 is 64 bit so there may be some difference there)
Hyper-V comes with a nice console (a bit like VM Ware <g>). It relies on system level drivers as well as a few services. The services you can turn off until needed, but the drivers you can't. And this causes the first point of angst for me... Sleep gets disabled.
Hyper-V's drivers disable Sleep for the main machine. You can't change this or toggle it which seems incredibly silly. Surely if you aren't running Hyper-V, your system should have it's natural capabilities in tact. At present the only work around is to install and uninstall the Hyper-V role (you don't loose your settings when doing this thankfully !), but this requires a reboot, and a fair few minutes. I really don't understand why the Hyper-V team didn't at least make it switch-able when Hyper-V is not running. Until they fix it, I think they should be made to walk/run to work rather than drive to make up for the carbon credits they are costing the world ;)
The next annoyance was XP had to be XP SP3 for the hyper-V extension to be installed which was required to get the network running. Of course without the network I couldn't download the SP3 onto the virtual machine (VM), nor could I do a network share etc. Hyper-V doesn't have folder sharing like VPC, and doesn't support removable devices like USB keys. So the only option I had was to burn a DVD (or create an ISO and mount that). This just seems incredibly silly. Getting files onto and off a Hyper-V machine is a major pain. It would be nice if it was like a physical machine where you can just plug in a USB drive
Finally, the display adapter for the VMs kind of sucks. It's a "Microsoft VMBus Video Device", which has a whopping 4MB memory ;) Obviously this means Aero doesn't work, and for testing any graphics intensive (or playful) application, Hyper-V won't do the job.
Other than that, hyper-V seems good. For development testing other than graphicic intensive applications, the big deal breaker is disabling sleep