[francescolaffi]

I found that a great keyword is 'dropbocks': I got 0.01€ cpc and a very good conversion rate. I maxed out several friend accounts spending 3€ each or less if I remember well. The keyword is great because it filters out who already use dropbox, if someone misspell it probably it doesn't have an account, otherwise with other keywords you'll probably get lot of people that already have an account clicking on your ads just to get to the dropbox login.