Hammocks are not heavy, and can be just as light as most ul setups if you do it right:
use 2/3 or 3/4 uqs instead of fulls
Use lightweight tq's
Use whoppie slings instead of straps
Use trail sticks as toggles for your tarp and hammock connections
Get/Make a cuben tarp(price but insanely light)
make hammock out of cuben(pricey but insanely light)
advantages of hammocks:
sleep anywhere there are trees (can also be done with hiking poles)
ease of setup
Way cooler than a tent anyday =P
stealthing is easier
pastes from other HF members on the topic:
"Last year when I was redoing my ground set up and was then tuned into the idea of hammocks as an option I made different choices for some items than what I had been planning for my ground changes. Now I had been looking at light weight things for the changes on my ground set up, a lither sleeping bag, a lighter this and that. But changing to hammocks brought top quilts into mind when they had not been being considered before that. Along with a variety of other things that got tweaked, adjusted or dropped from use at all. All in all, my hanging is lighter than my ground set up by a couple pounds. Hammock, tarp, and quilts just flat out are better for me than the tent, sleeping bag, and Thermarest. And I am more comfotable. Like others have said, the bigest down side is that the hammock is so comfortable, I want to sleep in it all the time. Wife has gotten to like it also but not enough to let me sleep out in mine all the time. Got to go inside and sleep in the BED. But I am looking for a BIG hammock for the 2 of us. "
"That said, there are several combos of hammocks, straps, large tarp, lines, state of the art, full length three season UQ, and two season TQ that will come in at 6 pounds or less...example JRB gear right of the shelf, BMBH, 11x10 Cat tarp, STLs, MW3 and Stealth quilts...there are many other combo's in this range easy...4 pounds is achievable if you use cuban and minimize each element.... Point is this is easily at or below the average ground tent, pad and bag or quilt combo and at comparable costs....Think about it... six pound for the entire camp easily puts one in reach of the 12 pound base UL standard...This means 5 day treks with a qt of water at sub 20 is easily doable...
Personally the only negative is not having enough trips to enjoy hammocking more."
and it goes on and on
my summer sleep system weight is about 3lbs, including tarp, hammock, insulation, suspension systems, guylines, etc.