Brian Shire has posted a new tutorial talking about some of the benefits of caching the functionality of your website (with things like APC, not file or database caching):

Opcode caches save energy, expenses, improve overall user experience on web sites, and it's often one of the simplest optimizations to implement. This article will explain the basics of installing, configuring, and tuning an opcode cache for PHP, the Alternative PHP Cache (APC).

The article focuses on how the APC works and how to get it up and working on your installation (as pulled from the pecl repositories). They look at some of the functions the extension's API includes (like ap_cache_info or ap_store for manual caching) as well as some more advanced topics like locking performance, working with TTL, cache priming and filtering.