It's strange to me how much linkedin is valued in silicon valley because to me it's like the ugly stepsister of social networking. Expecting someone to have a fully built out profile and expecting that person to actively seek out contacts in their own company is strange. I typically seek out contacts either when I first meet them or not at all. The only rhyme or reason to when I do it is when I happen to have a reason to be on linkedin. People are very haphazard about what their contacts look like. Some people have 50% recruiters, some people it's all friends, some people it's work colleagues, some people it's potential clients. Just because you know somebody doesn't mean that you are linkedin friends, and just because you aren't linkedin friends, doesn't mean that that person knows much about you at all.

I wouldn't trust social profile hunting as a real gauge for anyone's abilities. I know plenty of good coders that don't have github accounts because they aren't involved in open source at all. There are plenty of recruiters that don't know linkedin because they have other sources that fill their pipelines. There are people that build out their profiles specifically for job searches. There are others that won't build out a profile at all.

As far as back-channel references go, I'm not a fan. I expect references to be minimal because giving a reference is odd territory. A bad reference can result in a lawsuit, so why would anyone ever give a bad one? A TMI good reference can result in a lawsuit. People should stick to the basics.

The danger territory as far as I'm concerned is hiring someone at the tail end of a long group of rejects. You peel back your instincts in order to get to the finish line.