If you use Dropbox, this matters. I'm shocked that they added this arbitration clause to the Terms of Service, but they did. Here's the short version:
No matter what they do (delete your data, privacy breach, overcharging, whatever), you don’t get to sue. Instead, THEY get to choose the arbitrator according to whatever criteria they want, and thus any dispute is decided by someone they’re paying.
Also, you can’t join a class-action suit against them.