It's usually the Steve Wozniaks. Not always, but more often than not the technical gurus with mad skills are less enamored than their counterparts with doing what it takes to soak up the limelight. This isn't necessarily the technical co-founder (although sometimes it is, as was the case with Woz) but the geniuses that the technical co-founder depends upon. They are hard to find, and those who know who they are use them and play that hand very deftly. It seems non-technical founders occassionally feel its to their own advantage to keep them hidden too (lest they loose them), besides in my experience most non-technical founders underestimate the value of that person's contribution, and can even feel some spite that they are dependent on someone for whom they have less appreciation than they should. Such scenarios generally do not end well for the startup.