What are some best practices for optimizing code performance in PHP?

Everyone knows that PHP has such a bad rap for so much bad code being out there. I am a firm believer it is not a problem with PHP, itself, but rather the incredibly low barrier to entry (open source, readily available with nearly all web hosting packages, etc.) coupled with Wordpress (written in PHP) powering a large majority of the web, making it so easy for everyone and their mother to publish poorly written Wordpress plugins and spew bad code out there.

For those of you who are proud PHP programmers, what do you to optimize your code's performance?

For me, I cache. I use Memcached. I use Redis. I use Cloudflare's caching mechanism.

I use a lightweight MVC framework, and I rolled my own simple ORM.

How about you? ...