We wish to thank Fred Douglis, Tony DeSimone, and Sandeep Sibal for many stimulating discussions of caching issues and for valuable feedback. We would also like to thank Brian Larkins, David Kristol, and Doug Monroe for providing us with blinded access traces from AT&T proxies, and Jeff Mogul, Tom Kroeger, Carlos Maltzahn, and Digital Equipment Corporation for providing the same from DEC proxies. Thanks also go to the CRISP user volunteers and Darrell Anderson, Carla Ellis, Carmine Greco, H. V. Jagadish, Alvin Lebeck, Joe Shamblin, and Ken Yocum for offering comments on early drafts.