one of the most common ones is the AI cars slowing down for absolutely no reason, then coasting round the track, also on the last lap of a race, sometimes all the AI cars slow down for no apparent reason, you could be 20 secs behind and still win.
also, beware of pit entry's, if you soin your screwed, the AI tries to take you in backwards, and then the cra drives through the pit lane backwards, and stops before the pit exit for some reason :s
there are some smaller ones, but these ones are the only ones i have experienced, and only had the last one twice.
the first two seem to common for my liking