Too late but ...
I dove the "Blue Hole" (132 ft! My deepest dive!) Very cool, but you gotta keep your head as it's technical (in terms of time). A good master is an asset.
As for accomodations, I paid a butt load and stayed in a crappy crappy place on Amergris Key. There is poverty everywhere, and stray mangy dogs roam the beaches. If you are an animal lover, I seriously suggest going to the local mega-pet mart and buying a bunch of flea/tick collars (like 20) and when you see a (non-dangerous!) dog on the beach, be a nice guy and strap a flea collar on him/her!
My accomodations were like some guys "condo" that he rented out, even the resort where my friends stayed (a couple) were kinda crappy, imho. And they stayed at the place that accomodated the show "Temptation Island". I just hope you guys have a good place to stay!
Diving was great though, of course!
I was single at the time and I don't think it was really that "single-y". I hate to say it, but I feel no need to return, except for the diving. I'd rather go to Cozumel.
V