Rated 4 out of 5 stars
Not quite as awesome as I expected, because it doesn't allow you to capture the entire browser window, so not useful if you want to illustrate, for example, how a Persona looks in the header of the browser window (it looks bad, by the way, in the default FF4, unless you customize toolbars). So, it's back to Alt-PrtScrn for capturing all window content. Would also be nice if you could paste into it, among other things. It tracks the website visited, records the URL, and displays it on the Diigo image hosting site without asking. The program button should be moveable, like a normal toolbar object. I think it's useful for some things, just not as flexible or friendly as I expected.
Another thing: Using the upload to get a link feature, if you choose permanent link on Diigo, the image url is not permanent, but expired within a few hours when I tried to display the image on another site, and the temporary link only works as a link not as an image url for posting the image inline on another site, so not as useful for uploading as it could be. And I could not figure out how to get a usable link to the "permanent", annotated upload on Diigo, only the url going back to the original site.