The beginnings of emulation are already showing up on hacked PS3s.
Dreamcast emulator NullDC has a rough version running on Sony's flagship game system. There's a few screenshots of DC games running on the PS3 on dcemu. So far it's just the Dreamcast user interface, but it's a start!
The old SNES emulation standard, SNES9x, has also been ported to run on the PS3. The emulator it still missing a UI and save states, and the sound is broken, but it is playing games to a point where we can see them on screen. PS3 Evolution has video of Killer Instinct running on the ported version of SNES9x.
PS3 gets early SNES and Dreamcast emulation [engadget]