*I'm copying and pasting my final reply to Dropbox support, who told me to come here - Dropbox syncs on Mac even when the app isn't open.*
Dropbox should only sync WHEN THE APP IS OPEN. You have it running in the background now and didn't tell your customers. I don't want to have to click Pause Syncing every time I quit out of the app; I'm going to get busy, forget, and have things randomly syncing without my permission again.
I'm willing to bet the majority of your customers have no idea this is happening.
It needs to go back to the days before the Dropbox folder moved to the Library folder: app open = syncing. App closed = not syncing.
I'm a fan of only having apps open when I'm using them, so I don't want to have to wonder "Hmm, I wonder how Dropbox is acting today" every time I'm at my computer.