“The MySQL server now includes the widely used memcached in-memory caching system, and a plugin that allows fast NoSQL-style access to InnoDB tables through the memcached protocol. This access method avoids the overhead of SQL parsing and constructing a query optimization plan. You can store the underlying data in a single InnoDB table, or spread it across multiple tables. You can read and write data through both memcached and SQL. For example, you can do fast single-key lookups through memcached get calls, and do statistical reports across all the data through SQL.”

http://dev.mysql.com/doc/refman/5.6/en/news-5-6-6.html

We used memcached to great effect at Neowin, every time a logged in user hits the front page, we load the latest news information from the database, and display it, saving a rendered copy of that section of the page into memcached. When a guest hits the page, they get the cached copy, and no database access is required. We constantly have a number of logged in users on the front page, so the cache is never stale. It’s a great solution that lets us handle a heavy amount of traffic when we have popular stories (users coming in from reddit etc are usually guests, so the extra traffic adds hardly anything to the load)