I agree with many of the others... and yourself, that simply making the employees better informed as to why you are doing it is the best bet. I would be proactive about it (gosh I HATE the word proactive- it should be added to the other thread!) so that their "cause" doesn't gain momentum..

Your reason above about saving hard drive space seems wrong because the cache will just be filled with other stuff... the size of the cache can be preset - it is not dependant on content.

The way I look at it, quite simply, it is company's bandwidth and company computers. That's why I bought my own laptop and plug into the network!