I think shared blocklists are great. As defaults, probably not. I don't use any shared lists because nobody's going to take a serious run at me, I just don't want to spike my blood pressure seeing the egg/anime smurf accounts well-actually at me.

But I think network-effect block lists are probably a good idea. Nobody who follows Sargon of Akkad or other white-supremacist dorks is somebody I am ever going to want to hear from, so tube their tweets. That sort of thing.