What type of stuff are you wanting to know about. I have a GP2X and full version of GE I should be able to help you out.
The only draw back that I can tell you about GE running on the GP2X is that you can only get a max of 25 FPS right now. Mak is optimizing GE so the speed should go up in the future if not in the next version of GE.
He is also planning on rewriting the motor for the GP2X in the future also.
One other problem that I have found is that the GP2X uses a 16 postion (8 read locations) joystick comparied to most DPads that have a 8 position (4 read locations). So you haft to add extra code so you do not get dead spots on the controls. You can see what I mean in BearOids.
If you keep your game clean with out a bunch of background stuff running around you can get a game to run a solid 20-25FPS without too much trouble.
I overclock my GP2X to about 225 on the stuff that I have made. The only thing that I have posted right now is BearOids. There are some probs. with that one but you can atleast see a GE game on the GP2X. It is avail at
http://www.gp2x.de/cgi-bin/cfiles.cgi?0,0,0,0,30,2066
Also a cute game but not one of mine is
http://www.gp2x.de/cgi-bin/cfiles.cgi?0,0,0,0,37,1838
Most people can make a better game than what I have made, but I know nothing about C and I just wing it, kind of learn as you go.
I started making a new version of BearOids that runs alot smoother, but I have been to busy right now to work on it. I will get to it agian one of these days.
If there is something you would like to know, just ask. I will help you out with what ever I can. PM me or post here.