Copy backgrounds from Dropbox to Picasa for easy desktop-Android synchronisation
Set up email upload in Picasa (support.google.com/picasa/bin/answer.py?hl=en&answer=83342), and drop your email below. Make sure you have an album called "Backgrounds" in Picasa, and a "Backgrounds" folder in your Public Dropbox folder. Now you can set up a backgrounds slideshow in Windows 7, and have those same images show up in the Gallery app in Android. And you can add images to that Dropbox folder, and have them find their way to all your devices.