I'm noticing that sometimes the clip thumbnails on the time line will refresh very frequently- every time I reposition the CTI, trim a clip, etc.
I can't say that it's causing any problem, but I don't remember this occuring on prior versions of PPro.
Is this normal behavior for CS5???
Perhaps you are zooming in and out often and have the frames option turned on for the video tracks? Could you provide more detail?
Another thought - perhaps your disk is full or the media cache has not been cleaned in a while. go to the preferences and clean your media cache.
Hope this helps,