Apparently I was wrong about not being able to mod a Mac. Hmmmm, that's fun to say, "mod a Mac," also, it's very similar to Modemac.
Anyway, here's some stories I found about modifying Macs.
"Modders" Can't Leave Macs Alone
Japan's Growing Mac "Mod" Squad
Most of these Mac mods seem to be purely aesthetic, though. Mostly stuff like painting the case.
Oh, man, I want this. For Sale: A Piece of Mac History. If I only had an extra $25,000 laying around.