I'm not sure how long this has been available, but Pragmatic Books now offers automatic syncing to Dropbox. That means my Dropbox account will always have the latest version of my Pragmatic books.
I really like the Pragmatic model. They offer print on demand copies of their works as well as early access electronic versions. The books are very high quality and always well written. I only wish that the videos I've purchased could also be synchronized with Dropbox for offline viewing and streaming to my AppleTV.
My eBook purchases are always valuable to redownload through the Web site. However, my current copies could be out of date so I must remember to go get the latest versions.
However, once I configure Dropbox syncing, a folder is created in my Dropbox account
And after a bit of a delay, all of my eBooks are on all of my devices.