I gave a talk on a content-aware load balancer at PyCon 2012.

There's a video of the talk.

The zc.resumelb (source) is a content-aware load balancer for Python. When an application has a working set that's too big to fit in application cache, and when the applications data can be at least partially subdivided based on request parameters, the resume-based lb can provide significant performance improvements my spreading the working set accross different application workers.