In a new post on his blog, Lukas Smith warns developers working with autoload and byte code caches that things may not be as speedy as they might seem.
While it seems kind of nice one must be weary of the idea that they speed up your code. If you are running a byte code cache (which anyone who cares about performance of course does) you will get quite the opposite.
He includes a quote from an IRC log with Rasmus Lerdorf as to the reason why. Mainly, it has to do with the fact that autoload is runtime dependent as opposed to the byte codes which are handled and cached when working with apc.
So, what does this mean for performance? If you really want to squeeze those few extra bits of time out of the execution of your scripts, static includes are the way to go.