This banning of AdWords accounts that run traffic for Dropbox referrals is simply a reflection of Google's known hostility towards affiliate marketers. AdWords has been know to mass ban affiliate accounts and this is just another version of affiliate marketing without cash payment.
For those who still want to use PPC for Dropbox referrals, consider Microsoft adCenter, which has a much friendlier policy towards affiliate marketers.
For those who still want to use PPC for Dropbox referrals, consider Microsoft adCenter, which has a much friendlier policy towards affiliate marketers.