iOS: The official Dropbox app will upload new photos whenever you open it. But CameraSync will upload those photos in the background -- without you needing to open the app -- whenever you reach a specific location.
We've talked about CameraSync before, and it used to be a great way to upload your photos to Dropbox, Flickr, Box and other services with just one tap of a button. Now it takes even less than that -- just plug in your preferred location and it will automatically upload new photos to your cloud service of choice whenever you're at that location. There's no need to open the app, select your photos or do anything else -- CameraSync takes care of everything silently.
CameraSync is a $2.99 download for iOS only. The location-based uploads only work on iPhone 4 and up.