Facebook has done a really good job solving the problems of information overload and would provide a good model. The most important step is to group updates from each project. Right now half of my news feed is comments on a single repository. Those should take up only one or two slots.
The next step is to filter according to some metric of "interestingness." This is more challenging, but clearly solvable using machine learning (let us tag posts as interesting or not interesting to train the classifier).
I'd love to see GitHub make the news feed more useful. It's currently the most unpleasant part of an otherwise nearly perfect experience.