I've seen theremins housed in pickle jars, mannequins, doll heads, radios, trash cans, cat costumes, and now... Mac's.
Austin Dorkbot member Phil MacNutt recently demo'ed a theremin housed in a 1984-era Macintosh computer. No word on what model he used, but I'll bet he got a lot of OOoos and Woz...
Link: Get your dork on