I'll bite (and opt in).
As to the cliques: I didn't hang out at fiftychat during the heyday of the 'fiftychat mafia'. As I understand it, that was a clique, and it often acted as such in OT. But that's past tense. First of all, there's really not much activity left at fiftychat. And what there is, I've never seen any activity towards dogpiling anyone. There is discussion of people who are not liked, or even of people who sometimes are liked, and sometimes piss people off. So as a vector for OT cliquishness, fiftychat is in the past tense. Feel free to stop by and check it out if you don't believe me.
Then there's my own person clique, IALS. Now I know that I didn't do everything right in the setting up and running of IALS. But there were well over 200 people active on OT at different times invited to IALS. That's a bit broad for a clique. And anything posted there was fully visible to all the moderating staff. So you couldn't really plot against people there, even if you wanted to. That's not to say that people in OT were never discussed. But it didn't happen a lot, because it wasn't allowed. And as to who got invited and who did not, the primary criteria was always who just aggravated me so much that I wanted some space away from them. And, in any case, some of the people who I think are recent victims of the dogpile were people who did get IALS invites. And then, finally, IALS is dead too. So nothing is happening there, so nothing which happens there matters to OT now.
As to doing this by PM, I've received 2 PM in August which were not infractions, and 3 in July. Despite my huge post count around here, not much of anyone really wants to talk to me. So my opportunity to plot for the downfall of my enemies is pretty limited.
So yeah, I think dogpiling has happened. And I think it has driven away people I'd rather not see driven away. But if it's organized, I'm not seeing any sign of it.