Before leaving to Sinai/Red Sea vacation I had no choice- I need something really waterproof :-) So I made a quick buy based on my earlier experience with AquaPack products and bought their SLR soft case (waterproof to 5m/15ft). At the last moment I hesitated to put my K10D/16-45 inside while diving and chose a much cheaper alternative aka my backup set: K100D/18-55- and it worked like a marvel (and also did my Casio Z750 which I used as MPEG4 underwater video camera :-)
Setup looked something like that (with K100D with kit... sorry, bag is opened as I was too lazy to remove the strap now...)
http://www.diagnostika.ee/K10D/AQUAPACK.JPG
Although it is not an ideal solution, I guess that it is a rather cheap and comfortable one for snorkeling- and during 2 hours in water there was no sign of dripping inside the case (of course I had some packages of "Do not eat" moisture absorbers (silicagel I guess)
Best and happy shooting, JR