This article by Sheldon Brown may help you...
http://www.sheldonbrown.com/tyres.html
The whole page is chock-a-block with information, but I found this to be particularly intersting from your point of view:
"Butyl vs Latex
"Before World War 2, tyres and tubes were made from natural latex rubber, harvested from tropical trees. When the supply of natural latex was insecure during the war, a substitute, "butyl" was invented. Butyl turned out to be a very successful substitute, better, in fact, than latex for this application. All modern tyres and most inner tubes use butyl rubber.
"Some riders prefer latex inner tubes, because they can be a bit lighter than butyl ones. Some riders believe that latex tubes have less rolling resistance than butyl.
"Latex tubes are commonly a bit more porous than butyl ones, and need to have their pressure topped off more often."