Occasionally people I know invite me to join LinkedIn. Since I have accounts wilting at Orkut, Friendster and probably a few other network/social sites out there, I know myself well enough not to join any more of those. I even have a problem with email lists. If I don't REALLY want to participate, they become spam which I just shove into an archive and forget very quickly.
LinkedIn however promises something which surprised me. They announce that you can "reach a decision maker". I had to stop and think about that. First: If I was a decision maker, I would not be hard to identify for the general public. Why would I need to make a profile on a network site to become more available? Second: Let's say I had a profile on some kind of network software, would I want to be contacted that way? And last but not least: Would I trust the decisions of a decision-maker who was approachable through something like LinkedIn?
Joi Ito's now much-cited claim for WoW to be the new golf does however put me on the track of something here. LinkedIn, with the invitation policy, is supposed to be the same kind of exclusive community where you invite your friends and those you would like to have as part of your network into the inner circle. Like the two researchers' guilds in WoW you are invited to come play with the people who you would otherwise only read articles by.
It doesn't work the same way though. A golf club is exclusive because somebody are excluded and the participants contribute and risk something by their participation - if only a substantial fee. If you are contacted while at the club the person contacting you has been pre-screened, and is very likely to have useful assets you can then access at some other point. The contact becomes a valuable exchange of favours, if not mutual right now, there's an expectation of future favours included. LinkedIn invites us all to sign in. This means that the people you may want to reach will be contacted by a lot of people who have very little to offer in exchange, or if they do, they have made no commitment to the exchange.
I think systems like LinkedIn are interesting, and they most likely work great for the people who keep maintaining their presence and following up others. For people like me, who keep getting distracted by shiny phat l00t elsewhere (see that teenagers who do l33t speach? Women your mothers' age and up are doing it now, you can stop, it has become uncool), it's enough to be in the phone book. Which is where I find my old classmates, and quite a few decision makers, when I want to.