Dropbox is one of, if not the most used programs I have installed across my various devices. Now it gets even better.
From today users can now earn up to 16GB free storage from referrals, with the reward upped to 500mb per referral. What's even better is if you have already had some referral bonuses Dropbox are providing the reward retroactively, so you will also benefit in increased storage.
If you don't know anybody who might want to sign up... well... I am sure you can think of a way around that.