It runs onto the Pandora. But I wouldn't call it usable yet. It's ways to slow, crashy, uses thousands of files for saving the maps and the entire GUI/ icons n stuff are not suited for usage onto the Pandora. I find movement and overall "feeling" not that great, maybe because I played to much Minecraft onto the PC.
However, Minetest is a way in the right direction but I would prefer the real mobile MC that is already in Decelopment for Android Devices. It is written in solid C or C++ and already runs fine onto this funny Playstation phone thingy. I hope, notch makes an Pandora conversion one day, at least he has a Pandora.
Someone could try compiling Lamecraft, http://code.google.com/p/lamecraft/
It's a Minecraft clone written for the PSP but the author recently released the sources.