For use with just about any hammock I eventually end up with, how's this setup for up to 400 lbs (never likely to see that much in it, but a little insurance is nice. I had me, son, and 65 lb. dog in a hammock yesterday - over 350 for sure).
Hammock Bliss straps: ~3 oz., should be rated to 1200lbs or so.
AmSteel 1/8" Dyneema cord: 2 8-foot pieces only 1.5 oz and rated to 1800lbs or so. http://www.apsltd.com/Tree/d3000/e827.asp
Total would be 4 or 5 ounces. Add in two light 'biners and I'd have a very strong 6 or 7 ounce system that could handle trees 10' to about 24' apart.
Are there better systems? Lighter but with the same strength?