Ff18 has been out for a few weeks now so you can dig around and see how it is. I have been running it for a week and the benefits outweigh the few bugs.
As for bugs I've had a visual bug with the task launcher where it shows the current screen on the bottom until down to 3 tasks or less. Hard to explain without seeing it and doesn't affect anything. I get frequent freezes with wifi where I have to turn wifi off and back on again real quick to get it going again. This one is a little bothersome. I have also has to are add my quick camera links in the camera app 3 times already. Somehow it keeps forgetting what I put on the bar and resets to default.
That's really all I've noticed so far. GPS is much improved as well as all the google apps with ICS(talk, Gmail, YouTube, google+). Rotation animations are nice and can be speed controlled in developer options. Swype keyboard is improved. Browser is much improved. Everything is just all around better and faster. Battery life suffered for me at first really bad til I found dolphin sonar was the culprit, now it is back to normal. Btw with the sprint id app you can run the stock ics launcher which is awesome.