Well, I got around to installing the beta earlier in the week. It was a relatively painless process. I had a spare hard disk (it used to be my data store, but 160GB just isn't enough these days, so I bought a 750 for that), and just pointed the installer to that after booting from the install DVD. It took about an hour, all up, including downloading updated drivers for my Nvidia vid card & the onboard sound.
The only hitches were (1) that it picked the wrong monitor to assign as my primary (oh, yes, let's use the 17" screen as the primary, and the 22" as the secondary, that makes sense!), and (2) I couldn't see my WinXP drive anywhere in Windows Explorer.
Both were easily fixed - the Nvidia control panel let me swap the screens, while the disk management console (when I eventually figured out how to access it) let me assign a drive letter to the WinXP partition. I think that might have been an issue because it was a "C:" partition too. But there's no problem accessing it in Win7 now.
Generally, it works well. The GUI is different - the new task bar is much more usable - more like the Mac OS X dock. I still haven't quite wrapped my head around the new start menu, but that's because I've barely used it.
Armed Assault & World of Warcraft both work well, as does Firefox (including sharing the same profile - bookmarks, toolbars, etc - between the versions installed under Win7 & WinXP). I haven't run into any show stoppers yet. For beta software, Win7 is pretty good.
So, while I'm not entirely happy about the DRM / content protection side of things, that's not really an issue so far, as (a) I use VLC to play all of my media, (b) I don't actually have a Blu-Ray drive or discs, and (c) I can always boot into Linux... :-D
Actually, there's another issue - the Win7 installer overwrote the GRUB boot sector, so I'll have to boot off a disc to restore GRUB so I can boot into Linux.
Anyway, it's good to know that there will be a functional version of Windows for my gaming needs after WinXP goes the way of the dodo (which I believe is officially at the end of January - although you will still be able to get it in some OEM systems until May or June).