Firstly, in case you don't know, Dropbox is a cross-platform service for file sharing, synchronizing and backup. The application is free, along with basic use of the service (up to a limit of 2GB). However, by referring users to create a Dropbox account, both the user who is referring and the user who created the account get 250 MB extra space. Referring users allows you use up to 5 GB of space fo