Just ran into A Development Infrastructure for PHP which discusses a generalized strategy which Tony uses when building applications with PHP. He clarifys some of the design decisions further in the FAQ.
Think Tony’s done an excellent job – it’s an end to end view of the approach he’s evolved for building web applications and is also more or less a first – I’ve yet to see anyone be bold enough to describe a complete PHP architecture in this kind of detail. There’s alot of valuable insight in there and get the general impression of “sanity” (i.e. taking into account PHP’s inherent advantages and disadvantages). Think there’s plenty ammunition here for Marco.