Whenever I've gone camping I've always slept in a tent with those crappy, blue foam mattress pads that are about a half inch thick. I've always loved laying in a hammock on a warm summer's day. I've never even thought of combining the two.
I would imagine that the hammock is a more comfortable alternative to sleeping on the ground. How does the hammock hold up in bad weather conditions? Rain. Cold (I live in Canada, after all)