According to the Swiss security researcher who runs Abuse.ch, the use of free proxy services like Glype, Tor, and others have an option which allows administrators to log the traffic flowing through their proxy server on the Glype network.

FORBES: Use A Proxy Server, Feed An Intel Service

The MobileSpan Gateway is a central server application that acts as a transparent browser and document proxy on the corporate network.

FORBES: Advantages of the MobileSpan Approach