Here's a video of the Galaxy Tab playing a PSX emulator (PSX4Droid).
http://www.youtube.com/watch?v=gUq1nUrPoRU

The quality is quite good! I was expecting more slowdown due to the increased resolution, but it plays very smoothly! Hopefully PSX4Droid will get GL acceleration, rather than the software rendering it's currently using.

There are some incredible older PSX games that would be nice to play on the Tab -- especially RPGs.