OK, this is a bit of a weird one. Recently, my quicktime (with Perian installed) stopped playing AVI files - giving me the whole 'The movie is in a format Quicktime doesn't understand' business. This made no sense to me as AVIs were playing fine previously. Nothing I did could fix the problem. HOWEVER, just today I plugged in an external monitor to test something out; lo and behold, quicktime is playing AVI files just fine again! What's going on?! Has anyone seen this behaviour before?