Not sure why they couldn't separate spam in your feed from direct notifications...the later were 95% relevant for me once I hid everything from Mafia Wars and people sending me stupid presents.
At one point my friends were discovering new apps to spam notifications from faster than they could possibly be playing them. Blocking an app is no help when you have requests from a hundred different ones.
F.B. Purity
works well for that. Constantly posting articles about the security risks and general stupidity of Facebook games also helps to make it uncool (at least among my circle of Facebook friends) to play Facebook games. If the spam keeps up even after that, the friends are removed from my feed, or, in the really bad cases, unfriended.