The ONE thing that is keeping me from using CM9/AOKP is MISSED Calls. I would say about 1/3 of my calls won't even show up on the phone. My wife calls me at pretty regular intervals. I'll start thinking it's odd that she hasn't called, and all of a sudden GV pops up that I have a voice mail.
I'm a pretty "regular" guy, and my wife's last break at work is the same time every day, so I'm 90% of the time, in the same room. I know it's not an issue with the phone not coming out of deep sleep, since it would be awake while I'm reading the news or playing a game. It's not that the data is being tied up preventing the call from coming through, since I have tried to disable 3g, and run wifi only while at home.
This has been an issue for me on ALL ICS based roms, all versions of CM9 so far.
Things I have done to prevent it.
Full ODIN wipe to stock. Odin CWM, and immediately installed CM9 (Same steps were taken with each of the beta versions, as well as a couple of the AOKP builds although I don't recall which ones).
Installed GApps, and installed ONLY may necessary apps (google voice, G+, Capital One, OneNote, flashlight widget).