Tubular webbing tied with a tape knot is one of the strongest ways to go...by far better stronger than any reasonably sized rope with a knot in it.

And don't forget there are creative ways to get around putting too many load bearing 'bends' into a rope.

Here's an interesting bit of web information about failure testing done by a search and rescue team:

http://www.xmission.com/~tmoyer/testing/pull_tests_11_98.html