This is an awesome ROM. But, here are a few things I noticed:
1.) On my Optimus S, it's awfully slow!! CM9 is faster than this...and I'm tempted to say that stock Froyo is faster than this. HOWEVER, having installed iLauncher (which was likely intended for stuff like JoyOS) seems to have helped dramatically. UPDATE: Nevermind...now this thing seems to be running even slower than it was before!!
2.) The JoyMusic apk isn't completely compatible with Dem BEENZ (my corny nickname for JB); it plays perfectly fine...but when you tilt the phone into landscape mode to bring up the view of all albums, the app crashes almost immediately. And making this even stranger is that The SAMMICH (my corny nickname for ICS) didn't have this problem.
3.) And here's a rather ugly thing from CM9 that seems to have reared its head here: the deep sleep issue where when the device is in sleep mode, SOMETIMES attempting to wake the device fails no matter what you do...and a battery pull is the only course of action. And like CM9, this is at its worst while listening to music. (I've had this happen with the stock music player, that lame Apollo app, and the JoyMusic app...)