The Black Bloc isn't that effective in my experience(very limited experience mind you). We show up, do battle, normal folks on the street have no idea what's going on, then "everyone goes home".
The Black Bloc is a manufactured riot which is just as hollow as the manufactured town hall meetings the ruling class has recently decided to humor us with.
But in places like Greece and France it's another story. Large numbers of people take part in riots, both masked and unmasked, with clear demands and focused anger. what's going on in Greece right now can't be ignored, it feels like the real deal.
We can say though, the black bloc has forced the politicians to barricade themselves in four star hotel bunkers surrounded by a wall of riot police, but is that an accomplishment in the end? Those decisions still get made and the majority of people passively accept them. I can't tell you how many times I've got the question "What's a G20?"
But now we must pick up every piece
Of the life we used to love
Just to keep ourselves
At least enough to carry on