You can block those. Saved my sanity.
Yeah, that's all I do. I block the application, and usually end up hiding the person, too.
Even worse that the Farmville/Cityville/Mafia Wars crap is when old friends try to sell things using FB as their vehicle. Man, talk about tackiness.
I've already seen people hawking real estate, mail-order coffee, and various of health products. I'm just waiting for when someone tries to push Amway on the site. Now, that will definitely get someone nuked off of my friend list.