Am I the last one to figure this out? Really a fab bit of technology for us ereader ... er readers.
Grab a title (say Cory Doctorow's Makers) and hit the DB icon next to your format.
And the book's in your Drop Box and on your reader, if you have the app installed like I do on my Sony. Have to use the browser on my Kobo, but I do anyway to add new books.
Pretty darn nifty, Project Gutenberg