1.0 upto 1.5 can run homebrew stuff (basically you can run games from memorystick

2.0 can be downgraded to 1.5 so you can do the same

2.5 your shafted.. at present this cannot be downgraded and will only run UMD games

and the only game so far i cant run from memorystick is GTA as it uses movie codecs that are only on 2.0 and above