As I've previously said, I am a big fan of del.icio.us, especially when combined with Bloglines At the bottom of every post on this site is now a 'Bookmark this' link that links to the 'add page' form on del.icio.us and populates it with link information for the bookmarked post. If the user isn't logged into del.icio.us, then it'll reach the login screen.
(If I can come up with something snappy which makes it clear that it's a link del.icio.us I may change it from 'Bookmark this')
I know that not everyone using this site will use del.icio.us, but I hope that this will be useful for those that do.
Perhaps there is some way to change the 'Bookmark this' link in the same way that the RSS feed link (thanks to Aquarion) is 'intelligent'. It's beyond my skill, though!