[Updated 8:00 p.m. EDT, August 10, 2011: Well, that was a brief experiment: the Highlighter WordPress plugin was interfering with other features of the site, so I uninstalled it. Seeing that no one used it in the two weeks it was available, I don't expect howls of disappointment.]
As an experiment, I’ve installed Highlighter on this site. Select any text and you’re offered the choice of either saving it, commenting on it, or sharing it. Readers don’t need to sign up for a Highlighter account to comment on or share highlighted text, but they do need an account if they want to track and store their own annotations. Time will tell whether for purposes of this site Highlighter represents an enhancement or a nuisance. If you have any views, let me know.
And the AddThis buttons at the bottom of each post now include the Google +1 button and a Google Bookmarks button. Click the former if you want to help a post be heard above the online din. Click the latter to add to, or create, a set of bookmarks that you can access from any computer. And those buttons are in addition to a boatload of other AddThis share options.