Like many people I've managed to collect a few nice scalps on LinkedIn, but often wondered why. Luckily we have Guy Kawasaki to help us feel like it wasn't totally pointless after all.
Update: and now they publish your profile using the hresume Microformat. Cool!
I've been on LinkedIn for a while and while I've not used it for it for anything yet, I still feel it's a useful resource. I guess only time will tell.