I use Facebook and LinkedIn, and I recognize the merits of both. After signing up for a Kickstart account and exploring the service, I agree with other bloggers--it could prove useful to 20-somethings just starting out and looking to build a professional network.... But for those who have been working for a while--Generation X, for example--Kickstart is more likely a place to reconnect with old college chums. Gen X is better off sticking with LinkedIn for professional networking.
My two cents: Anything that helps college students and recent alums focus on professional networking is a great thing. It's not something all college graduates do well. More here.