I keep my iTunes library on a server in my den and often play it via the library sharing feature to my laptop (which then streams it off again to my AirPort Express, but that's irrelevant to this hint).
It's always annoyed me that, unlike when playing music locally, the remotely shared music's album art is not accessible in the lower-left corner window. I still haven't figured out how to do that (does someone else know?), but after installing iTunes 7 (I have no idea whether this works with iTunes 6), I was playing my remote library on shuffle. Eventually, one of my video podcasts came up in the shuffle. Since I set the preference to show videos in a separate window, iTunes dutifully popped up the playback window, but the interesting part was that when I skipped to the next track, the window didn't go away. Instead, the next song's album art appeared and continued to update with each song.
I've not seen any way to invoke this album art window other than playing a video, as well as having the separate window option for videos enabled. Clearly, though, it is not impossible to retrieve album art from a shared library. It now just needs to be more convenient. For those interested, I blogged about this with a bit more detail and a screen shot.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060914075221695