Multiply is another social networking service. A big crowd from Orkut is migrating over there. Some of them also use dotnode, tribe, and friendster - some people like to try everything or do it as research. But several people are switching for the sole reason that Orkut's servers can't handle the load - they are victims of their own success.
It's fun to watch the early adopters playing with this new tool. John Perry Barlow is already on there and has 131 contacts and, of course, they all look like very interesting people. Multiply uses different paradigms than Orkut, but has the primarily the same services. The groups/communities of special interest are still pretty small - I don't know when it was launched.
UPDATE - 8/18/04 - I just noticed that JPB deleted his Multiply account. It may have to do with some of the scuttlebut going around that Multiply claims rights to all the content you post. Also, another thing I didn't like about Multiply is, if someone is your friend, they can automatically see your email address. Dinah Sanders had an interesting post questioning their integrity/intentions on August 15th and others have blogged about it also. My personal take on it is that they're just sloppy. Either way, I don't think their product is all that great.