As always with Facebook, if you put in a bit of effort those things can be hidden from view forever.

Mouse-over the big freaking div, click on the little cross on its top right, and choose "Hide FarmVille" or "Hide Mafia Wars" or "Hide Doomaflotchie Widget", and you'll never see any updates from the damn thing again. Across computers. Which makes it better than Greasemonkey scripts or browser addons.