I recently spent a few hours smashing my head against my keyboard trying to figure out why PHP-FPM was dying every time I tried to load my favourite framework. The cause ended up being APC. Versions 3.1.9 and 3.1.8 don’t work properly with PHP 5.3.6 on Ubuntu 10.04 and Debian 6. I had to use APC 3.1.6 to get it to compile without errors.
Hope this saves someone an hour or two.