Grizz is right, back on the 1st page of this thread, the stock BB line with tree straps is the lightest option. The Whoopie Sling will add extra weight to the stock suspension. It would be the weight of about 10 extra feet of cord- roughly 0.8 oz or the weight of 2 SMC rings. For the extra 0.8 oz you get easy adjustability, reliability, no backup knots to worry about, security, quick setup and take down, and a built in drip line.
I'll admit that I am one of those ultralight gram weenies, but I'm taking my medication and I'm much better now! Seriously, I have had issues with the weight of a hammock vs ground shelter, but I've come over to the "dark side" and have decided that the comfort/site versatility/multi-use/LNT aspect of hammocks, more than offsets the few extra ounces.