What about the possibility that end-users' computers are breached?

- User/pass is saved in the 'Remembered password' area of browser (this is decodable by malware) - Email is screen-scraped by malware - Email is sniffed during login at a wifi hotspot (Password is encrypted, user/email may not be) - 3rd party apps that are linked to your dropbox account

I'm not saying that this wasn't caused by the database breach, but there are a TON of reasons that this could have happened. Some on Dropbox, some on the end users.

Don't expect your email address to stay private. That's what passwords are for.