Have several hammocks and been using them for years. Latest experiment for winter camping is to have two hammocks strung up so that I can put a second sleeping bag under me. That way, it doesn't crush down loosing insulation factor and it acts like an under-quilt. Then I sleep under another bag like a top quilt and a good sleep is had. It's a heavy system at around 10#, but it's the only way I have found to be warm into the teens without having massive condensation build up. Before I did this, I used the Hennesy winter bottom cover and my second bag had ice in it the next morning. I wasn't cold in the night, but packing out the extra water was a bear.
Also experimenting with the DIY bivy mentioned elsewhere on StP. I like the idea of a bedroll as long as it is the only thing I carry, so I put all my gear in the sleeping bag and roll everything up then sling the whole thing over my shoulders and go. I picked up a couple of ALICE packs with frames and am thinking about using one as a pack board to carry the bed roll. Should be pretty sweet.
For cheap hammocks, I am trying Owl Outfitters. I got a double hammock for around $30 or so and it's super light. It's been pretty cold so I have not slept in it yet.
In the tropics, you can't beat hammocks since any air flow will cool you down even to the point where you might even get chilled and need a light blanket. Just be sure to have a bug net though.