Phreaky from PS3 Attitude has this to say on trophies:
"Trophies, in their current iteration, do not work.
I realise that statement is a sweeping generalisation. It is meant to be. So go ahead and wipe the spattered coffe off of your screen and read on before spouting profanities at me and saying untoward things about my mother. I know she's fat.
The whole concept behind trophies and achievements is that people get trophies and lord over friends how awesome their gaming prowess is. For the most part this works really well. It's exactly what I shall be doing when I FINALLY beat Zico.