We would like to thank François Guimbretière for his ongoing contributions and George Francis, Pat Hanrahan, Eric Hoffman, Stuart Levy, and Al Marden for productive discussions. Anwar Ghuloum of the Stanford SUIF group graciously provided us with the call graph. We also thank the SiteMgr team at Silicon Graphics: Ken Kershner, Greg Ferguson, and Alan Braverman. This work was supported in part by Silicon Graphics, Inc. and the NSF Graduate Research Fellowship Program.