I know it's been done to death, but I'm really hating it right now. I've done it for 7 years so far and would rather do anything else in the world.
There are Mums not talking to each other, Mums gossiping about each others kids, a Mum I try hard to avoid because she gets involved in every tiny spat her angelic cherub gets involved in (and they are always best mates the next day after this woman has made a hugh drama over it), Mums who wave and smile one day, then walk past you to someone more interesting the next day. I've tried getting there early to chat to people, getting there at the very last second so I can just collect and run... and it never gets better. I fucking hate it.