Here's an interesting item.. UMAX has a new clone w/a PPC 604 @ 150 MHz, and all kinds of goodies, and it's quite a bit cheaper than a 9500.
Seems like they'd do better to go directly to a 604 @ 180 MHz, but they'll probably wait. It comes with a single processor, but has a special slot for a secondary one.
And in other multiprocessing news, Copland is supposed to support SMP fairly well, for up to 4 processors. Of course the multitasking implementation is such that current programs will need a bit of a rewrite to support these processors, but it should be a fairly decent threading system that will scale up to more processors without program changes.