If you are a user of Dropbox, you should enable two-factor authentication on your account. Dropbox joins Amazon, Google, and LastPass as service providers offering strong authentication for account access
Dropbox opted for TOTP, which is the Time-based One-time Password Algorithm. For end users, this means you can use Google Authenticator or other apps that support that; Personally I use Authy for iOS as my weapon of choice in managing my software tokens.1
I can understand why Dropbox decided to go with TOTP but would have preferred they went with Duo Security instead, even if it was just for paid customers. Duo is much more convenient! But the bottom line is that at least they offer multi-factor authentication at all for a service that stores important data for millions of users.
Edit 2013-02-18: Duo Security now allows you to add TOTP tokens in their mobile app. This means that you can use the fantastic multi-factor authentication via the Duo service and also store your tokens for services like Google Apps, Dropbox, and others in one place. There are advantages to using Authy too, and I’ll write more about that another time. ↩