I'm doing my first tour this summer and I'll be hammocking for a chunk of it. I bought a REI 55* sleeping bag and a thermarest sleeping pad with the ENO wings (big help and highly recommend). I also got a Sea to Summit bag liner (25* extra insulation) for cold weather. I've been able to do 50* with just the hammock/pad/sleeping bag combo. I did a weekend trip last weekend and it was 38*. Using the liner, I was able to make it through the night, but I was a bit chilly. The liner made a huge difference.
I have a Warbonnet hammock with built in bug net. The bug net does help keep some heat in...which is nice. I am a side sleeper and will usually switch sides at night a few times. After a few nights in the hammock, I have found it to be no problem to sleep. The pad doesn't go out from under me and I've slept quite well.