I found 32-Bit Vista quite disappointing and slow, only with Service Pack 1 it became usable.
I never saw a 64-Bit version of Vista "in the wild" until last week; I finally obtained a 64-Bit installation DVD with a slipstreamed SP1 from Microsoft and installed it on my Quad Core Mac Pro (Early 2007) with 8 GB RAM and an nVidia 8800 GT.
It was a royal pain in the neck to install Vista 64 SP1 on the Mac, mostly because Apple is not very supportive to that version of Windows, but it can be done even without Boot Camp and without support from Apple.
Once Vista was installed, I was very positively surprised how great it runs and how fast the 64-Bit version is - not only compared to 32-Bit Vista, but also compared to XP -AND- OS X Leopard. Vist 64 beats the crap out of its siblings and it also runs a good deal faster than Leopard. "Snappy" is the word marketing people like to use for this experience.
Sure, the user interface could be improved in many aspects. I don't really like the new Windows Explorer and the new Start Menu. But, truth be told, there's also a lot of space for improvements in OS X as well - especially the Dock needs a complete re-design.
I cannot say that I really have a huge preference for the one or the other system. It always takes me a few minutes to adjust to each system, but then it doesn't really matter anymore which I'm using. The applications and other tools are more important than the underlying operating system.
For me, OS X has two killer applications: Aperture (which I like -MUCH- better than Lightroom) and Scrivener.
However, and this is -my- opinion based upon -my- preferences, background and experience, I find OS X is the crappiest platform for software development that I've ever seen. From where I stand, Objective-C is not a programming language, it's an ugly abomination. And Xcode and Interface Builder are clumsy last millennium tools compared to Visual Studio. It's amazing that Mac developers get anything done at all with those pieces of crap. It also still perplexes me that everybody seems to believe that Cocoa is the greatest and most beautiful invention since sliced bread served by Olympian Goddesses. But the worst thing is: There are not even any real alternatives available that truly support the platform. (Yes, I know Realbasic, and no, it doesn't cut it.) If you want to create truly native apps for the Mac, you -have- to go back to the 1980s and put up with Objective-C and Xcode. Good old UCSD Pascal was more fun to use - and a more beautiful programming language, too.
Another killer argument for Windows is the abundance of freeware tools. On the Mac, I mostly use registered Shareware where on Windows I get similar programs and tools as Freeware. Filzip vs StuffIt, just to give one example.
And then, of course, there are games. Windows has them. OS X forces you to purchase an Xbox 360 /and or a PS3.
However, OS X does not show you those annoying bubble boxes all the time, which is a huge plus. On the downside, it annoys you with its rotating beach ball instead.
Ultimately, both systems only cook with water.