Jaan - great article.
Do you think it is better to have a separate button for each of the major bookmarking sites, OR would a single button from the likes of
Add This! Social Bookmark and Feed Button - Web2.0 Social Media Optimization do just as well while saving some space?
Another thing - if someone already uses a social bookmark site like delicious, surely they will be used to clicking on the 'tag' button on their toolbar anyway? Do you have any stats to suggest it is worth adding buttons to your web site at all?