Okay I hired a jet ski 20 years ago and it was a lot of fun BUT it is now 2012 and I do not hear a lot of positive views about it.
Tripadvisor has a lot of stories about this:
Phuket Forum: Another Jet Ski warning - Patong Beach
Thailand Forum: Big Trouble in Tourist Thailand
Phuket Forum: Jetski Saga... Phuket Gazette Article
Phuket Forum: Jet Ski scamming continues
Phuket Gazette has more:
Please think whether it is really worth it...
But the jet skiers did go and help the stranded in Thailand...