From PHPEverywhere:

I just visited SitePoint's Advanced PHP Forums, and spotted a debate on cache design. I only stumbled upon this because I saw that Manuel Lemos posted to this thread. Manuel has a unique way of writing that almost always guarantees a heated response. But Manuel brings up a good point. Most cache classes out there could do with better designs.

He goes on to address several (three) of the issues involved with the creation of the PHP caching system: making it multi-user, maintaining data integrity, and an application for testing the caching of your data.

The above suggestions sound simple, but as I've learnt, simplicity is not easy to achieve. In youth, everything is oversimplified or too complicated - real simplicity comes from experience. Unfortunately, it's only when we get too old and senile that everything becomes truly simple...