I am a fan of the Hennessy Hammock. I disagree a lot about the back pain comment. All of the current gen camping hammocks have you sleeping at an angle to the main axis. This means that your head and feet aren't tilted up much at all. Their big nemesis is the wind though, bring a good sleeping pad to keep your butt from freezing.
Ditto on what Dan the man said. I really like my Hennessey Hammock but don't use them in cool weather since you need good insulation beneath you. Summertime and desert, wonderful. The biggest advantage is you don't need a level campsite, just two good trees.