I've add the russian doll caching package to a project that I am currently working on and I have found that it is actually causing a performance decrease of about 20%. The templates that I am caching is a class roster, which contains information about the class and, via one-to-many relationship, student information. So, in a sense my test case is similar to Jeff's example in the videos. So my question is what are some guideline for when the caching directive should be used, since I am seeing that it will not increase performance across the board.
EDIT: I ran the tests using memcached, apc, redis, and the filesystem(this required some hacking around the tag issue). I also turned off the middleware in order force caching for my test. I used apache benchmark to run the test (100 request, 10 concurrency).