travian(http://www.travian.us/) is a good example of a larger scale game that runs in DHTML and it has a ton of issues with client side abuse. Just installing grease monkey in firefox opens a rather large door to all kinds of exploitative behavior. That said, they seem to keep the game somewhat functional since most of the exploits seem to revolve around automation of common in-game tasks and not direct violations of the internal domain logic of the game.
Keep in mind that this example is far from being run with only JS and relies largely on server side controls.
