I'm tempted to buy it on release. I'm running the RC at the moment and haven't used Vista since (I've dual booted alongside Vista) and I actually quite like it - I've not had any trouble running anything - my drivers work, and things are smoother. As for Fallout 3, it runs better for me too. Same for The Last Remnant, though I've not tried any other PC games (except the new Arkham Asylum demo, which seems to heat up my laptop...though I doubt that's a Windows 7 issue) but since buying a 360, then only games I'll be playing on my PC will be PC exclusive titles.
The taskbar I think is really sensible (and doesn't take long to get used to), sure it's Mac like, but it has the best of both worlds I think and the general OS layout is a lot better IMO than previous Windows OS's.
All I can say is 'wow' to the fact that I'm complementing a Windows OS, I was very pessimistic when Vista was close to release, although not perfect, Vista wasn't a problem for me, though Windows 7 is definitely better.
[edit]
As for DX11, I looked a little bit into it and it looks like it has some pretty cool features, though it looks like we'll all need to be upgrading our GFX cards again.

(Assuming game makers utilise it more the DX10, though with features like tesslation I imagine it being more attractive)