I've been thinking about this too - some sort of site that allows high-reputation users from trusted communities access to other highly rated people from other areas of expertise. Eg. if you've got great rep on Stack Overflow, you can join and ask for help from someone with a huge Twitter following. Users with high rep automatically have a lot of credit for getting favours, while new users need to earn credits by doing favours before they can ask for much. Very basic - but still maybe too complicated.