* Most of the really good devs I know and hire do not bother with easy metrics like number of tweets, followers, or StackOverflow points. They are perfect to paste together on summary reports and look "complete," but their absolute values or essence don't mean anything.
* The high numbers on public sites seem to be for two classes of devs -- celebrities, who you already know are celebrities -- and people with way too much time on their hands (if they don't work for an open source company, which most people don't). Most people have average values. If someone is on LinkedIn, I'm more interested to see if they have X hundred followers per years in industry up to some maximum lifetime value. I generally ignore recommendations.
* See http://news.ycombinator.com/item?id=3771286 for the discussion about what the number of points actually measures on SO, for example. It's a great site, but it's struggling to handle both breadth and depth of material well. High numbers does not necessarily correlate with expertise, just dedication. Maybe I want that skillset for a customer service rep, but I haven't yet wanted it for an engineer.
* I have shipped 20M loc in my career in 32 regions, and none of it is available on github or sourceforge. Most engineers are like that -- again, the public numbers are biased to certain individuals. Maybe there is a way for candidates to quantify the projects they have worked on?
* What I would love is a way to automatically assess FizzBuzz on candidates. I know there are some sites like interviewstreet.com that try to do this, but they don't yet have the critical mass like linkedin. And I fear, the moment they get critical mass then they'll become a new SAT or other standardized test that becomes too easy to game.