Somewhat similar to reframeit in the idea, but quitedifferent in the implementation, here comes WebNotes. Instead of  “scribbling in the margin”, this technology uses the (equally famous) Post’It metaphor.

You can write your notes in post-its which can be positioned anywhere on the page, or highlight specific highlight elements on the web page. A sidebar lets you organize and manage your annotations easily with a drag and drop interface.

This nice tool is probably better suited for workgroups or single users than broader social bookmarking applications. The annotations are only shared by email, when the user requests it, as opposed to “shared on the cloud” by default like reframeit.