Aggressive PHP Smart Caching

I'm a PHP developer looking for feedback on a caching approach I put together recently. It's informed by thoughts people have shared on this newslist and other places over the years. My goal was to come up with an extremely lightweight flat file caching system which solves various concerns about portability, speed, and specific feature implementations. Included is a wishlist I generated to explain the approach. The code is small, and documented, and easy to test for those interested. Feedback form attached to the following web page (but this newsgroup is as good a forum as any, too). http://technologies.babywhale.net/cache/