Sharing links from Dropbox is convenient, but it throws your username out there to the public. If that bothers you, Dropproxy is a web app that hides your Dropbox username and creates a proxy address for sharing with the public.
Just enter in the URL of the Dropbox file you want to share, and Dropproxy shields your username so the person you're sharing it with can't access any other public files. You can also share your whole public folder and hide your username.
Of course, you're handing over your Dropbox username to Dropproxy, but it doesn't need a password. If you don't want to make your Dropbox username public when you share files, this is a simple way to do it.