The PRISM/NSA blowout was the last straw to break this camel's back. I've been growing dissatisfied with the constant urge to check Facebook/Twitter/G+ all the time, I've also been irked by how my very personal information, posts, and communications were being used to make money for Facebook.
There were many things I've said to people through Facebook that I actually wouldn't like to have data-mined (no matter who's doing it, Facebook, AdAgencyX, or the NSA).
While my Google searches, email, and other "free" services are still used in a similar capacity - I'm also working to switch off of those.
Leaving Facebook has been the best thing I've done so far. I feel lighter and less heavy with the urge to check it ALL the time.