Nothing against communicating via Facebook, if that is your thing. But it is definitely not childish to not communicate via Facebook. Boycott is too strong, perhaps, but if you simply see no use for it.
Personally I am just old fashioned in that way, I still run my own email server. I don't feel too happy about my communications belonging to some mega corporation.
Also, I don't like having to log in to FB to get my messages, and in turn to be trackable by all the sites that partner with FB.
That's just my reasons - but I don't boycott it. If somebody messages me on FB, I usually reply. I just don't initiate communication on FB.
It's not a huge money-making opportunity, but it's the first step towards a path I've been wanting to take for quite some time.
It's not that I'm mining Facebook for jobs any more than I mine my phone for jobs... It's that by boycotting it, I cut off a means of contact that others might prefer. (And I could also appear childish or out-of-touch as well.)