My bug, just encountered, is weird rather than game-breaking: When instructed to play the guitar, my sim started spinning it around over his head. The sound is normal, and he's learning the skill normally, and his other hand is in the right position for guitar playing...but the guitar is rotating, and it doesn't even stop rotating when I pause the game.
I'm planning to suck this one up unless someone knows a fix (quitting and restarting didn't help, selling and replacing the guitar didn't help - I haven't tried resetting the sim yet), since it's annoying rather than game-breaking, but I hope it's not a symptom of something more serious.