After a ton of research last year, I purchased a Hennessy Ultra Light for my Appalachian Trail hike.

In short - I loved it.

My entire sleeping system weighted under four pounds! (Hennessy Ultralight is just under 2lbs...)

Some people are critical of hammocks because of the fact that you must find two trees within range. My experience has been that it's MUCH harder to find a flat and clear spot of soft earth for a tent!

I regularly strung my hammock over rocks and bushes on sharply angled ground. I like the fact that you can make camp with minimal impact on the plants and ground cover.

You must, of course, consider the issues hammocks have in cold weather (cold air flowing underneath you and sucking out warmth).
A simple foam pad in the hammock handles temps down to about 40F. Below that you need additional insulation on the outside. However, in a pinch you can simply lower the hammock down to the ground and sleep *as if you had a tent.*

Can't say enough about the Hennessey. It handled hot, cold, and very, very, very wet conditions with no problem. There were bad storms where I was sure I was going to get soaked... But with the fly properly set, there's no problem. Plus it's easy to set up in the rain - just pitch the fly first, then put the hammock up underneath nice and dry.

I have to admit, the first few nights being suspended like that made me a little nervous. I felt like a "bear tootsie roll." But I soon realized that in the very unlikely event that I had to wake up and run in an emergency, the hammock was MUCH easier to get out of than a tent. No zippers to find in the dark. Just sit up, shove your feet through the velcro seal at the bottom and drop neatly to the ground. (Then realize it wasn't really a bear at all. And change your shorts.)

I currently camp in a tent (my girlfriend wants to snuggle). But I do miss the comfort of my Hennessey. (Though not enough to leave my girlfriend alone in the tent...) ;-)