My wife and I will be spending 9 nights in Phuket in Feb 2008.

I dive and she doesn't. I have found some companies that will do a day trip to the Similans for diving. Is this reasonable or will it be a measurable day?

Any Dive companies suggested? We will be at the Marriott where Nautica Divers are. They have been pretty good in the past, but any other ideas are welcome.