[UPDATE]: Facebook plans to release a rewritten PHP runtime shortly. There was some speculatory report which made claims of a 10Ximprovement over mod_php.
Lately, I've managed to push myself to work on a new (and hopefully useful) pet project. For somebody whose constrained world-view of PHPLand was centered around producing or maintaining MVC frameworks that weren't full of shit bloat, It's been an interesting experience treading previously uncharted territory.
The most bitter truth is complicated
Let's accept it. PHP (for it's 33% share of the web, facebook, wikipedia, yahoo! and everything else included) is a tough nut to scale. The conventional way of scaling the PHP-layer for an application from scratch involves getting your hands dirty in the world of web servers, load balancers, opcode-caches and more.