PHP deeply needs some kind of persistent server
For bigger applications this becomes a necessity, the resources (memory and cycles) spent only for loading the code is already a barrier. Splitting up functions and methods (exactly! decoupling methods from their respective classes), so they are loaded only when necessary is the best way out without a persistent server.
Still the best solution would be a persistent server, for things like handling the database connection, loading up translations into memory for efficiency, handling most of what is called 'core' in php application servers out there...
There is Vulcan´s Logic SRM, still the problem is that we need something supported from the PHP main extensions, to assure every configuration out there will have support for this, or else we would have to develop for 2 different platforms which wouldnt work probably...