Vista will be amazing. It will be a pleasure to look at. You'll love using it, and it'll look sexy. Once you have it all set up, just like on a mac, it'll just work.
Leapord is going to look and feel just like Tiger, which felt just like Panther, Pumba, and Jaguar.
Chances are, OS X will crash on you just as often as Vista will crash (assuming you don't get viruses/spyware/etc.., which you don't get if you're safe about browsing the net)
Both OS's will contain bugs. Both OS's can be run on sexy hardware (my PC is silver and sexy)
In the end, I'd say Vista will be fine as long as it's not taxed too much. Windows has a tendency to crap out if you do a lot of CPU intensive work. OS X, although it'll be great as far as multi-tasking goes, won't be much different...a few new features here and there, but not the big jump like XP->Vista.
In the end, I'd like OS X on a sexy (not the blasé macBook/pro) laptop.