Been using 8 for about a week now... it's actually quite nice once you disable the tablet interface (there are a couple of different methods out there).
Honestly, it's already good enough to be a casual daily driver. I have yet to run into any program compatibility issues - unsurprising since "8" is really 6.2 (7 is 6.1, Vista was 6.0).
Defrag util now supports SSDs and runs TRIM instead of defragging:
File copy dialog has received some tweaks:
Collision handling is vastly improved, imo: