As mentioned in this new post on the Zend Developer Zone, there's a forum posting over on the YoungCoders.com website that looks to dispell the "age old" myth about Smarty - it's suposed bloated nature.
There has been a lot of talk about how Smarty, a popular template engine for PHP, is bloated and not useful because PHP is already a templating engine and that you're essentially creating a template engine out of a template engine. As everything I read could just say that it was bloated without backing up their statement, I decided to investigate it myself.
He describes what Smarty is and how to can help you and your site with compiled templates. There's a brief look at the syntax it uses and how it can help make the output of the site simpler than invoking PHP each time. He also gets a bit more indepth on the templating system, showing the process it uses to check the template and update if it needs to.
His conclusion? Smarty isn't that much different than any other kind of simple PHP-based templating language out there. So, what about the slowness? Well, he recommends checking your compiling setting - that's where the overhead is when the pages are loading.