apt-get -y install libpcre3-dev; sudo pecl install apc will totally replace apt-get install php-apc.
Both will install the APC extension for your PHP installation, there are however 2 differences:
Different versions: apt-get will give you the release as of Ubuntu-12.04's freeze (aka APC v3.1.7), while 'pecl install apc' will give you pecl's latest version (v3.1.9 as of now).
Visibility in the software center: Installing via pecl circumvents Ubuntu's integrated packaging system, so Ubuntu's apt/dpkg system is not aware of the updated version. In case there's an update Ubuntu may overwrite your side-loaded APC instance with an updated old version.