I went with Win7 RC (build 7100) over Vista and agree with all of the comments above. I definitely prefer it over Vista and look forward to the full release.
That being said, I've had a few minor issues:
#1 My Abit Airpace wifi card (which has horrid driver support and was notoriously a pain in the butt to set up on vista) did not work on windows 7. The abit drivers were not recognized as signed by win7 and someone ended up hacking the atheros wifi drivers to look like signed abit airpace drivers which solved the issue. I then had issues connecting to my wireless router which was corrected by fiddling with my encryption settings - i don't believe this had anything to do with win7 tho :P
#2 My computer would not shut down all the way (fans would stay on as would power to certain devices). This is another common issue for a few people with P5B mobos and it turned out that the IEEE94 controller on my asus mobo was not set to allow the device to be powered down which prevented shutdown from occurring fully. Once I went into the properties for the device in the device manager and adjusted the power management, the shut down options were fixed. (http://www.jamespaulp.us/?p=235
#3 I havent been able to get the VL System Mplay Home Center software to work properly which, again, isnt surprising because their support is horrid and I previously ran into issues on Vista. I havent bothered to mess with this one too much because I'm hoping to avoid using their cruddy software entirely if I can find the appropriate workaround.
#4 I havent messed with this too much, but I havent been able to easily install the mpc hc video codec - to register the codec in windows I need to run the regsv32r exe as an administrator, which is easy enough, but I just havent bothered to mess with it. The windows codecs seem work fine for h264 decoding (as far as my eyes are concerned, anyways)
The only real win7 issue was #2 which was easy to find a solution for. It boots faster, runs faster, and for the most part is very compatible with most hardware setups. I just happen to have 2 devices in my system with terrible driver support from the manufacturer.