FYI: last version of APC (3.1.9) fixed some memory leaks with FastCGI,
I have no issues with php-fpm 5.3.8 and APC 3.1.9
another recomendation - switch to PHP 5.3 if you can, 5.2 branch is not supported anymore, and php-fpm SAPI is now bundled into main PHP (5.3), works fine, just pay attention that config file is not XML anymore.