I stumpled upon Vladik Rikhter’s post via Hacker News on how to utilize Google Adwords to max out your Dropbox referrals for less than $10. Basically, you set up an ad campaign that leads people to sign up for a Dropbox account via your referral link, giving them 2.25 GB (250 MB extra for using a referral link) of free storage while you benefit 250 MB (or 500 MB if your account is linked to your school email). My initial attempt at this did not yield any clicks, probably because many people were following this method. I waited two weeks and I still didn’t get any referrals; this was probably brought forth by the publicity generated by Lifehacker’s post (see this too). After about 3 months of waiting, I raised my max bid to $0.10/click, and I got 5 referrals in a 24 hour period. I then raised my max bid to $0.20/click and I completed my quota in a day (I’m at 18.3 GB right now with my student email linked to my account). My total cost was $5.34 since I had many referrals prior to using the campaign (was at 9.3 GB). FYI, the default auto bid was around $0.14/click, so this amount should give you enough referrals in a 24 hour period.
Note to self: use Google Adwords when I need people to click on a link (e.g., for referrals).