Well, I did it. I put the Windows 7 beta on the laptop I use day in and day out. This machine had Vista on it, and the upgrade was utterly painless. All my software was still there and still working fine when the install was complete. The only glitch was that my built-in touchpad has become invisible in some way. This means I can't configure it to be less sensitive, which in turn means I was "clicking" a lot when I didn't mean to. I disabled it completely (using the 1980s-style UI of the edit-your-settings-on-boot experience) and other than having to carry a mouse with me when I take the laptop somewhere, there's been no other impact.
First impressions: I use jump lists a lot. Enough for a separate blog post. I like everything I noticed, except the default large-icons, no-text, group-everything setting on the taskbar. I fixed that:
(I've cropped it so it doesn't stretch the page)
I've said it before and I've said it again ... you can't really learn a product if you kick up a VPC once in a while but live your life in a different product. Windows 7 is stable enough to live in, and living in it will show what it's really like soon enough. I'm liking what I'm living.