I joined RocSoc in Freshers Week and never went... I also joined altsoc and have been to a couple of meetings but it seems to be mostly second and third years and hardly any freshers there so I don't plan to go any more, really. A lot of people join them and never go, it's nothing to worry about.
Some people really enjoy their societies though, so don't just think they're all crap from what I've said, haha.