Amiga (remember them?) is releasing a ATX form factor PowerPC logic board.
It's pricey, and I don't know what availability will be, but it will still be much cheaper than buying a Mac. A LOT cheaper.
It will have soldered cpu, G3 or G4.
Linux already runs on the board (in fact they used linux to debug the hardware) and I imagine Darwin will be on it pretty quickly.
Once Darwin is on it- that means we can build our ppc boxes for things that ppc is good at (like RC5).