Not sure about you but I have been on LinkedIn for a number of years now and always found it a useful tool for finding old work collegues. I have invited people to join and get invites to. To be fair I never used it in 'anger' to seek business. I did get a flurry of invites a few months ago but I do not proactively contact many people in my network.

About six weeks ago I got another Facebook invite and too the plunge. I am hooked. I love some of the neat applications but most of all I like the way it helps me keep in touch and know a bit more about friends - their interests, tastes and hobbies. Nothing too heavy but enough to know what interests them. I have already used it to seek advice about a book to read and a film to see. I also found out someone was at the same University this week as me also attending a summer residential course. They saw my 'what am I doing' and they posted that they were also here. Without it we would either have never have known or found out months later. I have also started talking to some people in a similar line of business as ourselves and with similar interests.

For me it works. Nothing too resource intensive. Not intrusive but with enough info to help start the conversation.

For another opinion check out Paul Walsh's blog. Also read some of the comments. (Thanks to Hugh McLeod)