[cdr]

It's not necessarily easy, but decoding MMO data files can be massively profitable for players. Reams of valuable data are often stored client-side to save on sending it during gameplay. You can maybe learn what items are in the game (including items in not-yet-released updates), where the items drop, and what the exact % droprate they have. You can learn the exact HP and other stats of mobs (if it isn't normally displayed).

If you mean extracting images, 2d image formats are pretty easy and 3d are quite doable. Things like http://kayin.moe/?p=2218 exist for some games.

[ultramancool]

Yeah, most often tools like you linked are built by partially reverse engineering (ie: with a disassembler and a lot of time) the game's binary though rather than a simple guessing-based method as the author used here.

[VikingCoder]

I'm still bummed that OnLive died. Seemed to me like it would have been the PERFECT platform to kill cheaters for MMOs that weren't twitch-based.