People have been using tor service webservers to release material as Anonymous.

Yes, it can be used for regular political activism, and sometimes is.

But the "four horsemen of infocalypse" are all there, ridiculously easy to find, but at the same time impossible to trace, and form a biggest part of onionspace.

It can be also taken as a proof of true Tor anonymity, though; the sites are all there, and the only thing law enforcement can do is to try to break the security of the sites and sneak for some info THERE.