[AnthonyMouse]

http://en.wikipedia.org/wiki/List_of_Macintosh_models_groupe...

All of the PowerMac G4s and PowerMac G5s from 1999-2006 spanning 350MHz to 2.7GHz were sold in multiprocessor configurations.

Maybe most programmers never worried about writing threaded software for them, but they certainly weren't uncommon.

[brigade]

Only the most expensive PowerMacs had multiprocessors; iMacs, PowerBooks, and iBooks vastly outnumbered those with top-end PowerMacs. Which also meant there wan't much point in writing heavily threaded programs unless specifically targeting high-end users.