Gigantic memory footprint with Zend. I love the framework - don't get me wrong on that - I code stuff for people using ZF all the time, it's awesomely stable and a real treat to add on to. But it also costs a lot in processing to use it. I decided to write my game (and probably any future ones) without a framework to reduce the overhead - and the reduction is very substantial. I understand enough about php to write my db adpators, session management, et al - and happily steal good ideas when I find them in things like ZF that make more sense than what I came up with. Just consider how many people you expect to have online at once and if you are willing to give each process (like clicking a link to a page) upwards of 3mb or more for ZF, go for it. If you want to keep the ram consumption in the realm of 250kb or less per process, roll-yer-own.
