Drop Memcached, Add More MySQL Servers | High Scalability

A very interesting summary of a different way of looking at things: rather than add a new layer with memcache, consider creating more shards to the point where all your data is running in memory. "Hitting disk is the problem. Shard more and get your data in memory."

http://highscalability.com/strategy-drop-memcached-add-more-mysql-servers