I have one for camping, you need a pad to stay warm in all but the warmest weather. This is generally true, whether you have a tent or hammock as was mentioned earlier. To really be warm and to cut weight, there are down quilts that you can get, one for underneath the hammock and one on top of you, but they're not cheap.
The only other thing to think about is where you are and if there are lots of strong vertical things to tie to, trees or whatever. If you're in the desert with no trees, a tent might be better. I suppose you could rig the hammock on the ground with trekking poles, but it would basically be a tarp and you wouldn't be suspended off the ground. I haven't tried this yet.