People are going to be 'networking' most intensely when they don't have a job or are worried about their current job. If there are fewer people looking for a job and those people get pulled out of the market more quickly, there's less money to be made from them.
LinkedIn earned their 100 million users by providing a professional networking platform where the users could choose who they network with. When the userbase has less of a choice regarding who contacts them, they'll abandon linkedIn as fast as a teenager terminating his MySpace account.
LinkedIn is incredibly successful in IT related markets, mostly in the US.
It's like when Amazon started, it was very successful selling to people involved with the internet in some professional capacity.
If LinkedIn can make $243M/year selling to recruiters and job seekers in a recession, what do you think happens when we have a global recovery and the inevitable hiring boom comes?