Yes, and I'm not in any of them.
Yes they do exist, with all the categories as mentioned in this thread. What does annoy me however is that when people make friends in their halls in first year, they tend to latch on to a few people and stick with them from this point onwards indefinitely for the whole of their degree, and this hinders their mixing with other people that they should be mixing with i.e. on their course, societies, the union bar, friends of other frinds etc. It's pretty pathetic to see a lab/lecture finishing and then everyone rushing off to meet their old hallmates.