This article on highscalability.com is a really excellent rundown of some of the options available for scaling a site to the heights of Digg. Ironically enough, at the time of writing the highscalabilitycom web server shows this error:
Unable to connect to database server
The MySQL error was: User highscal_admin already has more than ‘max_user_connections’ active connections.
I can point them at this really good article on how to avoid problems like this… oh, wait…