A mashup that is a cross of Geeklist (for credibility), StackOverflow (for topic listing and determining expertise) and this (to negotiate the details of getting people together) would be useful in those cases where one developer would like to spend 30 minutes picking the brains of a better developer.

For example, many a time I've spent 30+ minutes helping "orient" another developer with respect to backbone.js development.

However, right now I'm in need of 30 minutes to sit down and talk with someone who's implemented OAuth from the point of view of the API provider (not API consumer), and organizing your DB to manage developer accounts and permissions assigned to each "registered app" and it's hard to find the person whose 30 minutes of orientation would save me innumerable hours of research just to figure out what is worth knowing and worth exploring further.

Being able to accumulate karma based on spending 30 minutes here and there helping others and then spending it with others would be awesome. It would basically be a "productized" version of those "Offer HN" posts.