Has anyone tried Diigo?

Has anyone heard of or used Diigo? http://www.diigo.com/ It claims to be a “Web Highlighter and Sticky Notes, Online Bookmarking and Annotation, Personal Learning Network.” And they have special Educator Accounts

I ran across it in this Educause Quarterly article Engaging Students with Engaging Tools by Ed Webb. It’s mentioned several times and the idea of being able to highlight text within articles you bookmark for a group sounds very interesting. I haven’t tried it yet, though a Google search on “diigo education” found some interesting articles.

Another article about Diigo is here:
http://digitalresearchtools.pbworks.com/diigo

Please add your experiences or comments or alternatives here. Thanks