PC gamers will tell you that there is no other way to play a first-person shooter than with a keyboard and responsive mouse. If you stink at Call of Duty or Halo on Xbox 360 because of the console's controller, then the XIM3 is what you need.
The XIM3 is basically an adapter box with an LCD that lets you map the Xbox 360's buttons to any keys and buttons you want on your own keyboard and mouse. The unit's "Smart Translators" provide incredibly precise programming, tailored to individual games. A shooting game like Modern Warfare 2 is obviously going to need more precision than a tower defense game such as Plants vs. Zombies.
A price for XIM3 hasn't been provided yet, but Slashgear predicts it will cost more than the original XIM2 that was priced at $150. Is that too much to get that gamerscore up? Bragging rights are pretty important these days. Some might call the XIM3 a form of cheating, we'd like to say it just helps level the playing field.