I use LI for sourcing, but prior to interviewing candidates I don't review any social media until I have met and interviewed a candidate. I don't want to go in with any bias from the LI profile. 

I have LinkedIn Premium (~$60/month, less if you contact for 12 months), which provides me with unlimited views of profiles and inmails each month.  We will use LinkedIn for keyword searching of candidates.  I've found good, quality candidates on LinkedIn and if they are not currently looking, they at times will know someone who is.  People I've reached out to in the past have contacted me again when they are ready to look (think "planting the seed"!).  While I can't say I get a hire out of this every time, I've found it to be a great way to see what is out there and more successful than the traditional "post and pray model".   I'd love to hear from others!  Thanks for asking, Steve!