I can't speak for their twine, but Hemptique has some truly nice rope and webbing, combined with the absolute worst customer service it has ever been my misfortune to run across. If you can get some of their twine from a third party vendor it should be as nice as anything else out there.
I can't speak to long-term durability, since I haven't put it through long hard service, but I've made a tumpline in part and a twined bag from the mid-weight Cousin's Corporation twine that Wal-Mart sells and it is decent stuff. I've also used some of Hemp Basics' 170 pound line for the rest of my tumpline and for that rope I posted a couple months back, and I like it a lot. I just got some middle weight (48 pound?) twine from them, but I won't know if it is really superior to the Wal-Mart stuff until I try making something out of it. It is, however, 100% hemp whereas the Wal-Mart stuff has other natural fibers in it.
Another idea for thinner stuff is flax/linen thread. It is very strong, and will be better than craft store hemp twine for sewing things. If you need a thicker thread you could try twisting a couple strands and waxing them - I routinely double up the thread I have when sewing leather and it works fine, and with some more care in twisting it would probably work for tying stuff as well.
