I've been running Win 7 RC on the 10 for a few days now and it seems to run fine. I haven't seen any strange performance issues. I have the black screen issue as well, but it appears to be a "paint" problem, as in WM_PAINT, not a driver issue. The video display works perfectly for me in the applications I've run (including video), but at startup, it needs a kick to repaint the screen properly. Having used XP and Vista for quite a while, I don't really find anything that exciting about Windows 7. There are little improvements here and there, but for me they're mostly "who cares" kind of issues. I use my machine to develop and run software, not to play with gui gizmos. The new menus and desktop controls seem to be an improvement, but certainly not something I would spend money on. I generally run the apps that I need to run and then use them. I leave my machine running for days or weeks without restarting and just suspend or hibernate it at the end of the day.
Something I would like to see fixed in Windows is the network properties panel. I constantly switch between a network with a fixed IP address and others with dynamic addresses. It's annoying to have to retype my fixed address each time I need it because Windows doesn't save it. That's all I can think of at the moment.