"It is pretty hard to get lighter than the tarp, mattress, bivy system"
I think it CAN be.. but it is totally possible to remain below the weight of many bivy systems, as well.
Many hammock rigs are in fact, a tarp, mattress, bivy system, just off the ground.
I like that many of us hangers are doing so well in the UL range, its good motivation and inspiration for those who seek to go lighter with a hammock rig.
my lightest, most crazy set up is a WB traveler w/ whoopies, a zpacks hex Cuben tarp, and a summer UQ - all three for under 2lbs (27.5oz, total)
that's the weight of most commercial bivy+pad combos, without even adding a tarp.. ;)