I don't even use Internet Explorer, so I was very surprised when my profile included hundreds of megabytes of junk inside of my %HOMEPATH%\AppData\Local\Microsoft\Windows\WebCache directory.
I attempted to modify permissions of this directory so that no data could be stored inside, and that caused terrible performance issues and errors reported in the Windows Application event log reported by taskhostex which was running the Wininet Cache task object.
The solution was to run inetcpl.cpl and click on the General tab -> Settings -> Caches and databases tab, and then uncheck "Allow website caches and databases."
After that, I launched Process Explorer and killed taskhostex, which had open file handles to several files within this directory. I then deleted those open files.
I then removed write permissions on the WebCache folder for my user, SYSTEM, and for Administrators.
This allowed Skype and other applications to run without writing data to WebCache.