I've read a lot of articles about ZF performance and still can't understand, if I've enabled byte-code caching (APC), does it make sense to use some other tricks? E.g. disabling autoload and using one big php-file with all necessary classes instead.
I was surprised to find that this is the only question on the site tagged performance, autoload, php. What a better place than this to dispel the #1 autoload myth:
Modern, well-designed autoloaders won't break APC (or PHP 5.5's OPcache), and are not any worse for performance than require_once (except for the function call overhead, of course).
Why? Well, now we have spl_autoload_register, which lets you add multiple autoload handlers. This allows each third party library to ship it's own autoloader that knows how to load that library's files, and skip the rest.
For example, Zend Framework 1's Zend_Loader_Autoloader restricts itself to trying to load classes that start with a specific pseudo-namespace -- Zend_ (and anything else the user asks it to load). If it doesn't start with the desired pseudo-namespace, it simply returns and lets the next loader on the stack run. It also knows that it can find Zend_Foo_Bar_Baz in Zend/Foo/Bar/Baz.php, so it doesn't need to search the include path by hand. Like other modern framework autoloaders, it follows the the PSR-0 autoloading standard.
Any dependencies installed via composer also get automatically built namespaced autoloaders in the same way.
It's that include path scouring that makes poorly-designed autoloaders suck. You generally don't see these in modern PHP code. The intense filesystem stat calls that result from trying to find files are a frequent performance drag. Check out this presentation by PHP creator Rasmus Lerdorf, in which he increases the performance of Wordpress through benchmarking, profiling, and careful removal of slow operations like stat calls.
The require_once-everything-up-front from the olden days is is unnecessary when you're using modern libraries and don't have a sucky autoloader. It's only a major win when you disable apc.stat if you're using APC, or fiddling with OPcache's validate_, revalidate_, and enable_file_override INI options if you're using OPcache.
tl;dr: Unless you know that statting include files is your largest bottleneck, the Zend autoloader is just fine, and you don't need to resort to a require_once fest.