Might be showing my age here, but...
...over the last year or so I've seen LinkedIn change from a handy tool into a monumental pain in the arse. The GUI used to be quite clean and intuitive - now it's metamorphosed into some sort of Farcebook clone, with screen refreshes and pop-ups triggered by mouse-overs, dog-slow refresh times and an abundance of flashy (and Flashy) crap. The endorsements prompts would be a joke if they weren't so bloody annoying.
The ability to keep in touch with business contacts is certainly very useful - but that usefulness is rapidly being eroded by an increasingly user-hostile GUI (Gaudy User Interface).