I built my PC 2 years ago and started on XP home edition. I then upgraded to Vista Home Premium in the December as a Christmas Present and have to say that it ran perfectly with 2GB Ram and an AMD Althon x2 3.00GHz processor. A year later, I upgraded to Vista Ultimate through the Ultimate Steal and thought the extras were a bargin for £30. I alo increased my RAM to 8GB and changed to an Intel quad 2.4GHz and had no problems whatsoever with vista. It booted quick and was stable as XP was previously.
I then upped to 7 Professional on the 19th July through60;my employer and then to 7 Enterprise beginning of September and have never really looked back. While the system is stable, there are a few issues I have, take MSN for example, it has a slight annoying delay on it sometimes when opening a conversation or a wink and 'crashes' but comes back a second or two later.
My boot times have increased a little from Vista, but I was never really bothered by that. The best thing for me, is that Vmware Workstation 7 has come to be a saviour over MS VPC and XP Mode. Vmware makes it for me, especially with 7's lower RAM hoggingness. I also like to new UAC controls that no longer pester you for access to MMC and other mgmt consoles. A good OS all round!
D.