Ok, I have a little more information:
All the schools in Kent county, UK (pop 1.4 mil) go through the same IP address. So that's may thousand PCs. Most schools "have an ISA server on site running Websense". Websense appears to be some sort of gateway software, and I imagine that ISA is the Microsoft "Internet Security and Acceleration" Server. I have no idea if either of these products has the problems of Blue Coat.
Daniel.