I've completed Katamari Damacy on PCSX2. It's fully playable with graphics glitches here and there (polygon spikes).
Got it running at around 30fps give or take, on a P4 3.4GHz with Nvidia 7600GT video card.
It would run close to full framerate on any C2D CPU I guess.
I'm using the latest GSDX9 plugin, latest SVN beta build of PCSX2 and Pete's SPU2 (to make music and fx play smoothly @ low fps).
I haven't tested many games, but I know you can forget about playing God Of War, it's not working for anybody.
I have a Puzzle Bobble game running at full 60fps, but then that's 2D only.
Will try some of my other games later and add to this thread.