Reid Hoffman, former
COO EVP of Paypal, co-investor in Six Apart, good friend and generally smart guy has launched LinkedIn today. He and his team have been working in stealth mode and I've been anxious to use their service after all of the discussions with Reid about it.
There have been a bunch of networking sites launching these days like Ryze and Friendster. LinkedIn is more focused on business networking and has a bunch of innovations to make it more useful for connecting when you are trying to network seriously (vs dating sites).
Anyway, I have no direct financial interest in LinkedIn, but I may invest if I have the opportunity in the future. Reid is a business associate so this is somewhat a shameless plug for a friend. Having said that, I like it a lot so far.
UPDATE: The discussion has moved to the the wiki