Edit: Ok, that's a little bit of a loaded question. Key to the professional hacker / public face: blog, github / google code, twitter and activity in forums (like HN).

How to evaluate a potential employee / contract.. the above, plus LinkedIn, CV / references, portfolio and social networks (if they aren't careful with permissions).

Supplier.. google, twitter (#good / #bad tweets) and credibility of web site.

Partner.. lot's of face-to-face time.