Whether you like the term "Web 2.0" or not, everything it implies — the Web as a platform for user-generated content, information sharing, collaboration — would not be possible without one cornerstone technology: Memcached.
Think about it.
Memcached was released in October 2003 by Djanga Interactive to scale LiveJournal. Tim O'Reilly and John Battelle presented their definition of Web 2.0 at the first Web 2.0 conference a year later (their definition is published here).
