Well, the media here reported that they supplied help in communication, spread the wikileak document that surfaced here a few post ago, and generally have been a huge pain in the ass for Tunisian censorship.
Even moderately skilled hackers could be of huge help in a fight against censorship, and a few member of anonymous are more than moderately skilled. Also they doesn't post on 4chan anymore.
For the pirate Bay, you're plain wrong : they have a small sized political movement in Sweden, and a huge sympathy from the public everywhere in Europe, don't mistake them with 4chan.
Edit: Actually the pirate party have branch in a whole bunch of countries in the world and a few elected officials in few of them.
Edit: interesting :
http://www.rue89.com/2011/01/16/larmee-ne-tire-pas-lhomme-fort-de-la-tunisie-est-general-185923Summary : the army refused to fire on the civilian, and thus forced the departure of Ben Ali. The army is presented as independent and near of the poeple (due to obligatory military service) but the police (10% of the population) was with Ben Ali.
No one know who are the pillager (civilian or police agitators), my bet is on both with the most infamous incident coming from the police .
A link on the involvement from Anonymous in the revolution :
http://www.liberation.fr/monde/01012313297-operation-tunisia-la-cyberattaque-d-anonymous-aux-cotes-des-manifestants-tunisienshttp://www.bbc.co.uk/news/technology-12110892 in English this time.
EDIT : Ok, here are the anonymous behind these operations :
http://www.anonops.ru/