Billy the Fish
Technocrat
Never saw a lads holiday on Phi Phi Don but the reverse. It's a mixture and defiantly not a lads piss up. Ko Samui is for that kind of things.
I think it must depend on when you go. When I went it was full of pissed up aussies, that was mid jan a couple of years ago.
*Edit* I'm not trying to put anyone off because it's an amazing place and there are quieter parts, but in peak season they do cram everyone onto a small island and it does get rammed!