Dropbox has announced through an email to users on older versions of OS X that it will soon be discontinuing support for computers running Leopard or other older versions of the operating system. Users still running anything older than OS X 10.6 will need to upgrade in order to continue using future versions of the Dropbox app.
Users who don’t upgrade will still be able to use the web-based Dropbox manager, but will be automatically signed out of the Mac app. From that point forward, they will not be able to login back into the Mac client until they are on a newer version of OS X.
The changes will go into effect on May 18th, so users still have plenty of time to upgrade their software (or hardware, if necessary). The full email is included below: