Not that bad
I am a linux guy through and through. My primary work and piddling the day away on the web boxes are linux (Mandriva, with an urge towards Kubuntu). I have Windows Vista Home installed on a dual-boot machine at home and I boot up Vista whenever I have the time and desire to play a big FPS. While that limits my experience with Vista (there is some web browsing and other incidentals done while I'm there sometimes) the experience I have so far is mostly positive. No speed or resource problems that I didn't notice with any previous versions of Windows (dual core AMD 64 dual-core - I was jumping the gun and expecting 64-bit to take off more than it has, which is practically not at all). Besides the really annoying "Allow or deny" questions that I am hit with repeatedly when I want to install software or flash updates, etc, the only issue I run into is an OCCASSIONAL problem with a game. Right now, the only game in my recent clutch that refuses to work is Bioshock. No other issues so far.
On another happy note, one of the reasons I went ahead and "upgraded" to Vista in the first place was the spyware, spybot, and virus plague my previous windows versions suffered...and I am not foolish enough to simply run anything off the web, nor did I EVER check email while running windows (that is a job best left to Linux with its virtual absolute safety from malware). It got so tiring and annoying to have to totally wipe my windows install and start over again to clean off the malware that I finally jumped to Vista. So far so good...but give it time and it will accrue a huge ecosystem of malware too.