In this recent post to his blog Abhinav Singh looks at caching - more specifically looking at four different caching options: WP-Cache, APC, memcache and the query cache.

Ever since I changed my job (from Business Intelligence to Web development) and started working with my present employer, I have had a chance to work on a lot of scalable projects. From making my project to scale from 20 Million PV's to 100 Million PV's to development of an internal tool, the answer to all scalable applications have been caching. [...] Here in this post I would like to pen down my experiences while working with all the caching mechanism. Their pros and cons. What things you need to take care while working with them and every little tit bit which comes to my mind while writing this post.

For each of the four options he describes what kind of caching they're good for, what they can do and a few "gotchas" to keep an eye out for when implementing them in your application.