[ams6110]

Constitutional rights don't apply to Dropbox at all. They are a private entity. If they want to inspect your data, they can, especially if they have disclosed this in their terms of service. That's why I would never put anything sensitive (tax returns, etc.) on dropbox without encrypting in locally first.

[rmc]

Constitutional rights don't apply to Dropbox at all. They are a private entity. If they want to inspect your data, they can

This is one of the reasons the EU courts have found that US law is not at all adequate for storing EU citizens data. In the EU, the Charter of Fundamental Rights ("Constitual rights") do very much apply to your dealings with a private company.