If you hadn't noticed yet, the elsewhere links on the right are sorted in date order, with the most recently updated sites at the top. I wrote a little Perl script to check the sites every hour or so. One problem I encountered was that dynamically generated sites don't usually send the Last-modified: header, so you can't use that to check whether the site has been updated. Instead you have to retrieve the entire page and compare it to the last one you saw. (I don't actually store the pages, just a hash of it's contents)