About Vista, I really like it. It's a way improvement over XP. At least the recent versions, the first versions were all crap but Vista has improved lots over time.
Slow startup? On my machine it starts up faster than on my old XP. Now, this could of course have to do with being a new computer or because I don't have many things on my desktop.
I like the security in Vista. If I want to install something or change something vital I have to agree to let the computer do it. If you're not careful there are viruses that try to install themselves and Vista pretty much prevents that. I feel way safer with Vista than XP.
The only thing I don't like about Vista (well, one of the few things) is the Aero theme. It looks really ugly (with all the blurring and transparent). I can turn it off (and I have) but then I don't have access to a numerous amount of extra features that I have with Aero. So that sucks.
My friends has an earlier version of Vista. He constantly gets an error popup that doesn't make sense and so he can't do anything about it but it close the window every time. And sometimes he gets two warnings before installing things etc. But I don't.
All in all, if you're getting Vista make sure it's a recent version because it's way better than both XP and the earlier versions.