That's one of the three things that make them very attractive for subtropical camping, like what we get down here in Florida.
They're cool any time there's anything resembling a breeze, even above 80* F (note that "cool" is relative at that point; it makes it possible to sleep rather than being truly cool), they get one up off of the local arthropod population and underbrush (thick most places down here, both of 'em), and if you're getting wet from underneath in an hammock you have bigger problems than just getting wet (we don't get steady soaking rains here, usually; we get frog-strangling thunderstorms that build up a shocking amount of water in an hour or two).
As to the insulation "problem", it's pretty easily solved at temperatures above freezing. Shug's videos are a good place to start; he has a "beginner how-to" series that starts here. Once you're done with those, a good place to look for more information is Hammock Forums. Be aware that information overload may start there; they're just as big of gear-heads as BPL members are, just with different specializations.
Fair warning: I'm a member over there as well, under the same screen name of "FLRider", so I may not be the most disinterested observer.
Hope it helps!