This is a slightly extended version of an informal and anecdotal talk that I gave at Grinnell College on March 16, 2001, and again (with revisions) on April 13, 2005.
This document is available on the World Wide Web, beginning at
http://www.cs.grinnell.edu/~stone/essays/keeping-stuff/

This work is licensed under a Creative Commons
License.
created March 11, 2001
last revised April 12, 2005