<nit> Sign-up page username field. When I tab out of the field, I get the message of "This username is still available", ok, good to know, but I think it would be better if you only chimed in in case of an error. My first reaction before I squinted at my monitor to read the small text, was, uh-oh an error message. </nit>

look forward to playing with this. I have a lot of workflow oriented around bookmarking.