I have to disagree with you on with the cliques, in my case. It was clear that at least 3 groups of people that I sat around wanted to talk to nobody but each other. No matter how much I tried to join the conversations, I was dismissed with chair turns, funny looks and flat out ignoring me (and the girl I was sitting next to who was also trying to "fit in"). After 6 months of this, I left.
While I agree that it's hard to get to know people you only see a couple of hours a month, it really isn't that difficult to include a newbie in a conversation or make them feel welcome. I didn't feel any more part of the group after 6 months than I did on the first day.