Dropbox gives you 250 extra mb. Yeah, but I (the person being referred) never heard of dropbox and would not have known if there was less or more MB. Unless

Dropbox gives you 250 extra mb. Yeah, but I (the person being referred) never heard of dropbox and would not have known if there was less or more MB. Unless Dropbox is smart and shows you the benefit of signing up with this special referral gives you a one-time chance to get more free space than usual. That increases urgency and therefore conversion rates.