Not in a social capacity. It's clear Facebook is the biggest engageable network but does that mean the best? It depends. Recently there have been a few articles about recruiters coming to Facebook over LinkedIn as more of the population uses it and more often. However what many find is that people reject this interaction on Facebook... as a personal based network people don't want those professional requests coming in, nor can recruiters find people easily given the privacy lockdown on most profiles. It's the wrong medium today, but of course Facebook is working to open things up and change that.
Take a B2B manufacturer like Caterpillar. Many of their blue-collar customers use Facebook in their personal lives but professionally? Not as much. As a result CAT runs their own forums, blog and works in other niche sites to engage and with great results. They're in the big networks too, but different opportunities in different places. http://www.businessesgrow.com/2011/05/18/case-study-caterpillar-and-blue-collar-social-media-marketing/
LinkedIn is a great fit for recruiting and viewing profiles but they have an issue -- stickiness. People sign up, fill out their profile, update their profile, add connections, but while groups, answers and other sub-features have helped bring them back, the interaction frequency is painfully low compared to more topical or personal sites.
On the other hand, leading B2C brands have established large social followings on Facebook [as well as Twitter and niche groups] and bases with increasingly strong results to product development, support, commerce, indeed their business is evolving from the interactions.
Most businesses benefit from using all the networks but which is best, or which to focus on, depends on what you are doing, who you are reaching and what engagement means for you.