Gonzalo Ayuso has a new post to his blog today looking at the performance of PHP exceptions and how it could effect your application's overall speed.
Sometimes we use exceptions to manage the flow of our scripts. I imagine that the use of exceptions must have a performance lack. Because of that I will perform a small benchmark to test the performance of one simple script throwing exceptions and without them.
His (little) benchmarking scripts are included - both looping 100000 times, one throwing an exception and the other not. The results were pretty obvious - the memory usage was about the same but the speed was about ten times faster without the exceptions (in PHP 5.3). In PHP 5.4, however, the numbers were closer as far as time to run. Obviously, unless you make super heavy use of exceptions, you're not even going to come close to something like this (micro-optimization anyone?).