Reason to upgrade?
I had Vista foisted on my with the purchase of a new PC - but you know what? After I got used to where everything was (and after SP1 sorted out some of the bugs like file moving inexplicably hanging) I have actually grown to quite like it.
The UAC nagging is the only remaining annoyance; otherwise it's reliable, stable, fast (on a Quad-core Q6600; 3GB RAM - nothing special) and good to look at. All my old peripherals from my previous XP machine worked fine so maybe I was lucky, but still - no complaints.
With 7 looking to put Vista into an early grave (and I understand why MS need to do this for business reasons) I'm faced with the decision of whether to upgrade or just stick with Vista until I next come to replace (or do a major upgrade) on my PC, by which time Windows 8 will probably be on the horizon.
I've no use for the touch functionality; Libraries sound pointless for anyone who actually stores their files sensibly in the first place; I don't like the idea of the new taskbar (I've never let windows 'stack' open instances of the same app - give me a separate tab for each so I can see what I'm doing) and alt-tab in Vista is fine for task switching...
So yeah, if this was a free Service Pack for Vista I wouldn't object to it, but I can't see any reason to spend money on it if you're already a Vista user.