I have a GP2X MK-I with the dpad mod (the default stick gets replaced with the pretty nice ngage QD dpad).

I think the gp2x and the n800 arent comparable due to the different focus.
the linux on the gp2x is very basic. no real applications apart from the included media player.

The big bonus is how much mature software there is. dozens of very good emulators (snes, megadrive, c64, amiga, neogeo, mame, atari st, etc.), many many native games good game ports (duke3d, gravity force, cave story, etc.).

thats what the gp2x is about. playing games/emulators. and its superb for this. it has a cheap plastic case, AA batteries and only 320x240, but it has superb free software.