i'm with don...i have the canon s330 also.  when i leave my hotel room which
is air conditioned, i leave the case open with the camera removed.  it almost
immediately exhibits condensation from the cooled hotel room, but by the time
i'v finished breakfast or just as i get on the boat, everything is it the same
ambient temperature and the condensation has disappeared.  at that time, i
seal everything up in the case and don't remove it until i'm back in my hotel
room.  i've never had a problem or needed the anti-condensation liquid that
canon supplied with the camera.

i believe the case offers a bit of magnification, so that anyone who is
interested can preview my pix right thru the case while on the dive boat.

as far as the silica gel is concerned, i don't believe it would fit into most
dive cases as they are usually very tight to the camera body and have lots of
moving parts...i think it would be a bad idea to try and cram one of those
packets ino a u/w case.

btw, anyone have any experience with canon's latest, the s-400?