The other podcasts on Desire are located here: http://www.swingercast.com/SwingercastForum/index.php?topic=1728.msg15848#msg15848
I've stayed at only one other resort in Cancun and Desire blew it away. (pun intended) The accommodations at Desire are very good and you should be able to really enjoy yourselves.
Best time to go? Better not ask me this one.
The week after our Desire Los Cabos trip, the resort was hit by a hurricane. Three weeks after this last Desire Cancun trip, is when this current Flu controversy hit. With that said, I may not be the best predictor but I'd say the summer months have very high temps.
I'd look for a group that is going about the same time you plan to travel and try and hook up with them. It is so much fun to travel with a group. (Especially ours, hint hint. Hope to have details about a 2010 trip soon.)
RE: Where to get it on....Allie and I had sex on the beach on one of the beds right under the nose of one of the guards. Others in our group told us they had sex on the beach during the day without a problem. Of course there is also a lot of daily sex happening in the beds near the Jacuzzi and at night in the playroom behind the bar.
RE: Clothes. The theme nights are fun but the guys have it way easier than the ladies. Our friends (and sponsors) at Play Passions have put together a good resource for theme wear here: http://www.playpassions.com/wardrobe/theme-wear.html?cat=98
Have fun and be sure to ask anything you like. There are wonderful people here that can answer any questions you have.