This is a really smart idea that produces very interesting data. Unfortunately, clipmarks, a favorite bookmarking tool of mine, is not measured, because it requires a client browser plug-in to be installed and thus can’t be included by the AddThis widget. A surprise is that google bookmarks is as popular as del.icio.us, but its functionality and usability is far behind del.icio.us, digg, and clipmarks.

From the user experience point of view, the AddThis button could be more dynamic. The icons on the button could be clickable, so that there is no need to pop-up another window to choose the bookmarking site. This makes the bookmarking experience more convenient. For example, the small bookmark icons on the button could be displayed based on the user’s profile, current bookmarking choice, and aggregated popularity. If the user logins to AddThis, the user’s preferred bookmarking sites’ icons will be on the button as shortcuts. Otherwise, the last bookmarking sites that were chosen on this browser session will be on the button. The "…" icon will pop-up a window that contains all other icons that are not directly accessible on the button.