Another option is to use Amazon Mechanical Turk:
http://codyaray.com/2010/10/dropbox-referrals-using-mechanic...
Also, here's the Dropbox page to get additional space by connecting your social networking accounts: https://www.dropbox.com/free
Also, here's the Dropbox page to get additional space by connecting your social networking accounts: https://www.dropbox.com/free