CM9 is usable, but far from perfect
short list of pretty big issues:
-no video camera
-no video chat
-opera mobile doesnt work
-no hw graphics acceleration - google chrome doesn't work, etc.
-a little sluggish in some areas. Especially Google Maps.
-Data is really weird. Sometimes it will break after a reboot and it's difficult to get it working. But once its working it will work great until you reboot again.
That said, I am currently using it. But debating going back to something like eclipse bcause of sluggish perf in some areas and no video.