And site visitors who would use these bookmarking services like Digg or Furl usually know how to add items to their accounts and don't need your favicons.
There is however a neat one-size-fits-all solution [a live example is shown above] called the AddThis button. It supports most bookmarking services and feed readers. You can either use AddThis on your webpages or inside email messages.
The interesting part here is that Add This provides statistics to bloggers about what content is collected the most on their website, blog, or email messages. That's a big advantage over competing sites like Feed Button.
For surfers, AddThis can help you reduce the Bookmarklet clutter on your Browser toolbar by consolidating all the social bookmarking icons into a single icon. Give it a shot.
Add This! | Screencast Demo | Browser Button