I ran 4.0 via Cyanogenmod 9 on my Nexus S 4G for weeks, and unfortunately the bugs and constant app crashes got so bad that, as much as it pained me to do so, I went back to 2.3 yesterday. I love Android 4.0, but there doesn't seem to be a good, stable implementation of it yet.

Example issues:

  * Random reboots
  * Choppy playback in the Music app 
    (Amazon MP3 worked fine)
  * Random app crashes, particularly 
    games (possibly due to lack of official 
    4.0 support)
  * Poor GPS performance, occasionally taking 
    15-20 minutes to acquire a position (typically 
    solved more quickly by rebooting, but it takes
    several minutes to know there's a problem in the 
    first place)

It's difficult to blame the app crashes on the OS if the app doesn't claim to officially support 4.0, but that's still reason enough to wait.

I'm eagerly awaiting the day that CM9 is released, or MIUI releases their official 4.0 version, but until then I think it's better to stick with what works.

Edit: Formatting.