Many people use Dropbox these days because its a handy file sync tool. However the paid service is quite pricey at either $10 per month or $100 per year for their 50GB package.
The free 2GB package is well used. You can get 250MB of extra space for every person you refer, up to 8GB. In other words, you can have up to 10GB of space for free through referrals.
And it also happens that Google Adwords are giving away $75 free advertising coupons like they’re candy.
Combine the two, and you can run an Adwords campaign for Dropbox using your referral link for free. As people sign up, you get bonus space.
I just did it myself, and for about 2 days nothing happened. Then tonight all of a sudden 10 referrals have rolled in as Google have activated my ad campaign. I guess I’m staying up until I get up to my 8GB which should be very soon.
The following video is a good guide on how to do this yourself: