I'm still having some issues with my CS5 install but I really haven't taking the time to look into a fix. There's nothing major just annoying little things.
The good news is that some of the features are wonderful. The quick selection upgrade with the "Refine Edge" tool" is great. "Content Aware" is remarkable. I've tried the "HDR Pro" but I'm not quite sure about it. I've used Photomatix for so long that HDR Pro seems slow. I'll give it some time and more testing before making my final decision.
The guys from NAPP did a week long series of Webinars showing all the new features in CS5. They explain them better then I can. Watch it here.