I've got an issue that seems to have cropped up around the time iTunes 8 was released (but I can't say for sure exactly when it started). I view my Music/Movies/TV Shows in Grid View. I have a rather large library and whenever I scroll up or down in my library the album/movie/tv art shows up blank and then it slowly re-loads the artwork. The artwork will stay cached for a while but if I leave iTunes alone and then go back, scrolling through my library will result in blank artwork and waiting while it re-loads the art. Why can't it keep a consistent cache of the artwork? Anyone else have this issue?
Edit: I just noticed that if I'm in a different Space and then switch to the Space where iTunes resides, the artwork is gone and has to re-load.
The only think I can think of is that my iTunes library is on a USB drive connected to my Airport Extreme.