Hi,
I have a small patch (2k lines) at http://p.defau.lt/? Jnc0Y1AY0hc0SNOhmFtzSw
that eliminates most of require_once() calls and uses require() in __autoload() handler. Generally it makes things faster, as less require_once means less stat (), as well as that might be more APC-friendly.
As well as some refactoring was needed, I could introduce lots of bugs. And break extensions of course.
As included source is executed at function scope, rather than file scope, various other issues could arise - like missing global declarations, etc.
So, please send your comments ;-)
Domas