I'm on a mobile device, so I'm having trouble directly replying to post but I'll tag the people I'm replying to: Blutooth and M8808.
M8808 - sorry, wasn't me though I did have a very similar conversation with somebody else studying the same subject toward the very end of the month. Commiserations on your rejection though.
Blutooth: I was on the Irish IMO team. It's a considerably easier thing to achieve than to get on the British one (roughly equivalent to the gap between Britain and the USA). Hence I'm not sure how much Cambridge valued it. I'm pretty sure I was rejected on the basis of my interviews - I was really nervous during them and hadn't slept at all for two nights before. My memory is a bit fuzzy but I think at one point I claimed root 2 didn't exist >.< Also I put nearly no effort into my UCAS application generally - my PS was the work of 25 minutes.
My situation is a bit odd - I'm home-educated.