Rewriting the Web with Greasemonkey, Rails and WEBrick
This architecture could be easily adapted to add private bookmarks to del.icio.us – or to add any number of cool features to any number of other sites. Here’s another example: Google’s Desktop Search integrates results from your local drive with the search results page on Google. Using greasemonkey and a local web server tied in to OS X Tiger’s Spotlight indexer, you could add this functionality to any search site you wanted to. Just be sure to lock down the web server to only serve requests from localhost, to avoid sharing search results for your data with anyone on the network who can see your machine.
Lots of great GreaseMonkey scripts over on the wiki. I wonder if I can use this stuff to get comments (optionally) showing up in the RSS feed.