Their internal subwoofer is actually fairly decent, so with a good set of speakers it can make a nice little audio station. Plus, since it can accept IDE hard drives, a drive spacious enough to store your entire MP3 collection can be installed without issue.
With the TV Tuner card, and a VCR or something (since normal broadcast TV will soon disappear), they can also be used for light video duties; kids usually don't complain about watching The Brave Little Toaster on a smaller-than-60" display.
They're fairly competent machines under OS 8.6 (which can run the earliest versions of iTunes), though hard-core gaming is kind of out of the question. StarCraft and Diablo play decently on them, though.