Interesting, and very close to the implementation of Etags.<p>On the upside, it means that files that haven't been changed won't ever be rerequested without needing a round trip to the remote server.<p>On the downside, you clutter up caches with "dead" but not yet expired files, and you have to deal with scripts every time you change files, which is likely to decrease the reliability of your site and provide a new point of failure.