I installed the 64 bit version and since it requires that drivers (which are loaded into the kernel) be signed it couldn't load up my 802.11 NIC.
I found out that the check could be disabled when going into the F8 menu at boot time though. This however is only for the session so you have to remember to turn it off each time you reboot.
The system feels solid and moving around Windows is very responsive (much more than what B2 was on my machine).
I had some trouble installing
Fahrenheit, which I recently scooped up from the bargain bin at the local game shop, but this I can live with.
For me the dealbreaker is that I cannot run Virtual PC 2004 on Vista and I live in virtual machines all day since I'm a SharePoint guy.
As far as I know I'll have to wait for Virtual PC 2007.