I have been (ab)using SiteBar for a while now and for me it really has become the answer to the question of how to track all of the useful sites you visit, ever.

They have a hosted version of their software that anyone can sign-up for or you can download the software as I have done and have your own installation (My SiteBar).

By far the most useful features are the firefox plugin (or integrate with your browser here) and the ability to email bookmarks to friends…someone asks you for a site, a quick click and they have the link

The only improvement I could add to this program is automatically checking the links to see if there is a broken link in the collection and emailing you to inform you of this, but I may write some code for this if someone has not.

Take it easy