As other have said, using an UQ and hammock system can be very bulky, I use a DD Frontline and Snugpak UQ. I find it's not really the weight that's an issue (as all of my other kit is ultralight) but the bulk, once you've got sleeping bag (even a good UL one) Hammock, Tarp and UQ and cook system, you've barely got any room for Food/clothes for a long trip. I managed a week canoeing in Sweden this year with my full set up and a 60ltr rucksack but it was pushing it, also, the food for the week was in a barrel in the canoe. If I had to carry it, there would be no chance.
We walked Hadrian's wall a couple of years ago and I had to give up hammocking as there was no way I'd have enough room for it, and I wasn't willing to get a bigger bag. Managed to get my total bag weight (inc food/water) to 13.4kg which I think is pretty good.
Anyway I digress, ultimately you've got to weigh up is the extra "bulk" worth it for the comfort, and for me it is. If you come to love hammocking you'll never look back. If you're just starting out with the UQ scene I'd definitely recommend the Snugpak synthetic UQ - they're 50 quid off amazon and as most people have said are plenty warm enough for almost all the british weather can throw at you. (assuming your sleeping bag is also up to the task). If, like me, you do most of your trips in the UK I didn't want the hassle of worrying about whether or not it's going to rain (because lets face it...it probably will!). If it gets wet your down UQ will be next to useless, at least a synthetic one still retains a lot of it's warmth. It's cheaper. And the synthetic bags are getting that good now that they are not THAT much bigger than the down ones (so to me the only benefit left is the weight saving, which to be honest. isn't enough for me to justify the extra £150+ it would cost to upgrade to a down bag) just my 2 cents worth