On the Unravel the Music blog there's a recent post about using memcached to held reduce the load on your PHP applications by caching certain parts of your pages.

Many framework and standalone PHP developers are given options to do full-page caching but partial page caching is rarely an option. Many times a sidebar or a footer that is loaded with dynamic content can be cached for 5, 10, or even 30 minutes without needing to read from the database again. This can drastically reduce the load on the server as query results for certain portions of your page are stored temporarily. [...] Memcached can store queries that have been processed and the bits of HTML that go with their presentation. Read on for a detailed example.

Once the memcache functionality is installed, its a snap to get right into caching your content. The two examples - pushing data in and pulling it back out - show how to cache a bit of HTML content to be used later.