I've set Dropbox to upload photos and video from my iphone to the "Camera Uploads" folder at Dropbox. I've been keeping the photos in that same folder and moving videos out to another Dropbox folder named: "Camera Uploads Video". This way, I can keep the photos folder "local" and the videos folder "online only" (to save hard drive space).
For some of the videos, I may delete them or move them to a folder on my local harddrive for editing.
This is what's problematic: Dropbox will re-upload some of the videos from my iphone the next time it sync's (to the "Camera Uploads" folder). It doesn't re-upload all of my videos, just some.