PHP is a widely-used Open Source general-purpose scripting language that is especially suited for Web development and can be embedded into HTML. Its syntax draws upon C, Java, and Perl, and is easy to learn. PHP runs on many different platforms and can be used as a standalone executable or as a module under a variety of Web servers. It has excellent support for databases, XML, LDAP, IMAP, Java, various Internet protocols, and general data manipulation, and is extensible via its powerful API. It is actively developed and supported by a talented and energetic international team. Numerous Open Source and commercial PHP-based application packages are available.
Plug APC all you want - it is cool, but apparently you have very little understanding of what Smarty is and what it does, because otherwise you would not have said what you have.