It's also worth considering that most big sites have more web servers than MySQL servers, and I'm sure Digg is in that boat as well. Doing your sorts on 20 fron

It's also worth considering that most big sites have more web servers than MySQL servers, and I'm sure Digg is in that boat as well. Doing your sorts on 20 front end nodes instead of 2-4 MySQL servers is obviously going to help improve performance and scaling of your MySQL servers.