linkedin is quite different from Tweeter. It's a serious digital place where you can find people based on their interest fields, professional background, etc. I think it's quite useful.
People who just want to show off in the net use to se other different tools, like Orkut, MySpace or Tweeter.
This is not the case. I managed to find and get in touch with many people through linkedin - but, yes, it's much more intended for professional purposes than leisure...