When trying to enable this module using Drush, I get this message:
Module apc doesn't meet the requirements to be enabled. The APC module needs the apc extension see: http://www.php.net/apc. (Currently using APC Not available)
If I enable it through the Modules page, I don't get any error message and APC shows up on the Status Report but the apc.php page doesn't show any entries being cached, except for apc.php. That might be too many problems for one issue, just wanted to give the full picture. I'm running a LAMP server, Ubuntu 12.04, PHP 5.3.10-1ubuntu3.1, APC 3.1.9.