Dropbox also screw over paying customers who use shared folders. (Yes I complained, but they kept explaining it was for freeloaders repeatedly ignoring "paying")

If for example you and someone else both pay Dropbox for 50GB each - ie Dropbox is being paid for 100GB of unique storage - and then you share some folders they deduct their space from your quota. As an example if they share 20GB of folders with you then you'll only be able to have 30GB of your own unique storage and between the two of you there will only be 80GB of unique storage.

Do paid sharing with a few more people and you'll quickly be out of space.