So... I downloaded the latest beta of Windows 7 (Release Candidate, Build 7100) and so far I like it a lot. But I've noticed you get a very different experience depending on whether you do a clean install or an upgrade install.
For my ASUS 1000HD Netbook:
I did a clean install. The operating system boots in under 40 seconds and reports 57% memory free after boot. The application compatibility is a LOT better than the beta 7000 build. The Intel GMA can only display a hint of the Aero interface effects, but the standard interface is pretty and perfectle usable. Applications seem to run as fast as WinXP. (Aero Experience is 1.7)
For my Compaq laptop 2.0 GHz dual core):
I did an upgrade install on this one. Because the computer has a 256 Mb nVidia graphic chip, the operating system was able to show the full Aero interface. However, most of the Vista sluggishness carried over into Win-7. The computer still boots a lot faster than plain Vista, and the system reports 45% memory free after boot, I think it's pretty obvious that you get more bang out of a clean install. (Aero experience is 4.7)
For both installs, however, the application compatibility is quite good -- even with picky apps like Second Life.