Actually, as long as you avoid virus ridden operating systems, I've found PHP to be very cross platform. Of course, the biggest problem is getting all those other packages it uses like libgd, to compile on Solaris or HP UX or whatever. Just stick to Unix and you've got great cross platform capability.
But hey, you've already made up your mind, so stick to your own perfectly transportable app server. In fact, why not find a support forum like this one for it, and then you could just go away, I surely wouldn't miss all the astro turfing.
