If this is the way that iTunes is designed, then the design is flawed. The reason I say this is because the other MP3 manager I use on a regular basis (MediaJukebox) has absolutely no issues at all dealing with the library of this size. Scrolling is instantaneous, searches are very, very quick and the overall experience (at least with respect to the responsiveness of the interface) is much, much nicer. I would boot iTunes altogether if it weren't for its superior iPod support, and of course the Music Store.
And good guessing on the size of the iTunes library files. The .itl file is 22MB and the .xml file is 28MB. That's not that big... iTunes should put those things in RAM and do some intelligent cacheing and I should have no issues.
One other thing, this is new as of version 5. Version 4 handled scrolling fine, even with the large library. Something changed, and changed for the worse.
And no, I don't have the artwork window open.
Frustrated in Denver.....