The biggest trend in Internet right now is social networking, I believe. There are lots of applications specialized in social networking, and all hot new applications must have a social networking component in them.
LinkedIn is the second social networking service that I used. The first one must be Koulukaverit.com. LinkedIn seems quite professional, business-like, and dry. Contacts are mostly defined in terms of work relations. It's a way to stay connected with old colleagues and if somebody changes their job, you can see it there, but that's pretty much it for me.
If you know me and want to connect, you can find me there by my name.