Here is the new provision in the new terms of service:
We Both Agree To Arbitrate. You and Dropbox agree to resolve any claims relating to these Terms or the Services through final and binding arbitration, except as set forth under Exceptions to Agreement to Arbitrate below.
From now on, you’ll be using the American Arbitration Association if you have a dispute with Dropbox. Oh, and no more class actions, either:
No Class Actions. You may only resolve disputes with us on an individual basis, and may not bring a claim as a plaintiff or a class member in a class, consolidated, or representative action. Class arbitrations, class actions, private attorney general actions, and consolidation with other arbitrations aren’t allowed.
Presumably, this would include things like a disagreement over whether Dropbox should have given up your files to spy agencies or law enforcement without a fight.
Don’t worry, though, you can opt out — but only until April 23rd. (It doesn’t look like the opt-out applies to the class-action waiver. You’re just SOL for that.)