We have W7 running dual boot to XP home - and so far, so good.. thankfully, the audio/mp3 issue we have with W7 means that we'll just have to make sure we're in XP mode first...
Bar from that, it's running sweetly, its behaving and there have been several 'Ooo.. lookit daaaaat!' moments.. especially the minimised windows thing... where, if you hover your mouse over the preview pane, you can expand it from there rather than expanding it manually (Vista.. great preview pane, lacking in function - W7 addresses that

)
Plus there are other neat functions too - too many to list, but it's fun finding them out
I'm SO tempted to see if my ultra-old PC would even look at the W7 distro - just out of bloody-minded curiosity...
The alternative route would've been installing bootcamp on the macbook and seeing if that could handle it just as well...
Either way, for me - it's just like handling a souped up and tweaked Vista - they've sure as heck made it quick to load - I won't argue there!!
But it looks pretty, and I've read reports that some people have been able to run W7 on computers with 1Ghz processors...but don't quote me (or them) on that!
For those of you with a computer thats 2 - 4 years old, I'd say its probably worth a shot if you think your computer is up to it...
I do believe that M$ will be putting a version of W7 on some laptops towards the end of this year too...
It's all looking good here...
Until the next Beta release