Adobe Buzzword is available, no need for private invite to use it. It took me couple of minutes to register, then I checked out Buzzword; I must say Buzzword rocks!
It has a usable, fast, responsive and sleek user-interface (UI). Buzzword also allows to save documents in different formats (.doc, office-xml etc).
It allows to insert images, tables, comments, notes etc. I loved the ui-interaction for each of these features. I don’t know how to express in words without showing the screen-shots, so why don’t you check it out
Just wondering, who designed the user-interface of Buzzword?