free and easy to use, it's a professional networking site. One of my clients invited me and I ran into all sorts of peeps. Anyway it's free so what the fuck?
The reason it's free is all the fucking spam from headhunters who as the result of linkedin now don't have to read your CV and thereby target positions you might actually be interested in or qualified for. Also the lame asses you are glad got fired last year will be all over you for recommendations.
If you are looking, it's a useful tool. If not, it's a pain in the ass. Register with a free email account instead of your real one, at least.