I have been using Windows 7 for over 6 months now, and I have to say it seems very stable and very usable. It is Vista done right.
The biggest problem with Vista was the lack of driver support at release, which basically meant having to buy new peripherals if they were any older than a year or so. And the annoying way they set up User Account Control - every time you did something it asked if you were sure, a couple of times.
With Windows 7 they have got much better driver support in place, including an automatic lookup via the Internet which actually works in most cases, and they have simplified User Account Control so that it is about right and not so annoying that everyone will turn it off.
UI wise it has some improvements over XP (which is now 8 years old - although patched a few times since its launch) such as hovering over the taskbar icon will give an active thumbnail and so on. Also, the Media Centre actually picks up the EPG from the channels which my Vista version never did. Multi-monitor support is supposed to be much improved in Windows 7 although I don't run such a setup.
Also, it actually has lesser hardware requirements than Vista and in some cases will run better than XP on existing hardware.
So yeah, go ahead and get it.
