Somewhat disconcerting that I am a Dropbox customer, yet neither the breach nor the explanation has been communicated to me by email; I've had to find out about it by reading HN.
There is no way dropbox would be able to explain to them what happened without scaring them silly.
And if nobody logged in, there can't possibly be any danger to their account.
Opposed to who? People who do know what it means and should be scared silly but aren't because they've been beaten into submission by breach after breach after breach.
IMO, this is reflective of a corporate culture that places testing and security on the back burner. And while some people may be OK sending their data to such a company, the rest of us might not be.