Enough has surely been written in this forum about LinkedIn and the importance of being listed there. I won't dwell on the importance of being there, but if you're not, GO DO IT RIGHT NOW!
If you use the system actively, it can be a great way to reconnect with clients, colleagues and frieneds. When I first joined, I went through a personal database and send out invitations. The results were fun and even received a few thank you calls.
LinkedIn provides a great additional way to stay in touch with your connections and you'll be adored if you take the time to write kind recommendations for them. For example, Brian Brady, a great mortgage professional, and I recently exchanged recommendations and I am more likely than ever to recommend him for mortgage loans.
(this is a test to see if Brian really reads my posts or not;-)
My recommendation? Go to your LinkedIn account and start recommending and writing nice things about your connections.
Then watch and see what happens!