Dropbox recently reduced the number of devices I can link to my account using the free plan to only 3 devices. While I understand that I should not complain for something that is free, I am no longer recommending dropbox for anyone. This includes paying customers.
Dropbox, may I suggest a device limit of at least 5. 10 would be better, but I could work with 5. The whole point to your service is to sync devices, so why cut your own throat?
For now, I am changing to Google Drive for my cross-platform sync and sharing.