In reply to baldie:
Used as a tie-in and called the "competition knot" in that context, the ring bend is an esoteric alternative to the usual knots.
The primary use of the ring bend, also called a water knot, is to tie slings from webbing. Since over-the-shoulder slings are nowadays almost always sewn, the ring bend is pretty much relegated to tying webbing slings for rappel anchors. This is a common but unfortunate application for the knot, because under cyclic loading, the ends of the webbing creep into the ring bend, and if an end creeps all the way in the knot can fall apart.
It is safer and more considerate of others who may use your anchor to tie webbing with a double fisherman's knot, although it is bulkier and not as attractive.
Lest anyone think ring bend failure from end creep is merely hypothetical, there was tragedy in the Tetons last summer in which a highly qualified IFMG-certified guide fell to his death when a tether he had constructed from webbing tied with a ring bend came apart.
http://www.rockandice.com/climbing-news/gary-falk-ifmga-guide-falls-to-deat... .
I have personally encountered rappel anchor tied with ring bends, at least one of whose ends had already disappeared into the knot. Since it is so common to knot webbing rappel anchors with ring bends, it is essential to inspect the knots before weighting the webbing, ideally while still on rappel and so fully protected by a connection to a separate anchor.
