This is a feature of the iPhone Dropbox app that I use all the time, but keep coming across people who haven’t found it yet, so it’s worth a post! The scenario is: you take a photo and want to get it on your desktop quickly. You don’t want to plug in the iPhone, open iPhoto or Image Capture and download them.
In your Dropbox app, click the camera icon bottom centre and choose ‘existing photo or video’ (or ‘New Photo or Video’ if you haven’t taken a photo yet), choose the item, and you’re done. You can bung it in anywhere you like, but as my work folders sit in Dropbox, it means I can drop it in the relevant project folder, or a public album in ‘Photos’.
By the time you open Dropbox on your desktop, it’s already there!