References and testimonials, LinkedIn, Zerply, Github, et al? Maybe I'm too suspicious; if after an initial interview I got a stream of emails from an applicant's buddies/colleagues that I didn't ask for, I'd wonder why he felt he needed to coerce them to do so. I also think it's a bit dangerous to latch someone's technical skills to their social aptitude. Everyone has friends, not everyone thinks it is professional to sweet-talk a founder on your friend's behalf. I'd love to hear what others think, though.