Rasmus Larsson has a recent post to his site showing how to build a basic templating engine in PHP that uses the "__toString" to help render the result.

Possibly the most common sign of bad code is tight coupling, especially between logic and presentation. It might seem like a good idea to print out the HTML while the data is being generated, but it more often than not leads to a big incoherent mess of tangled code. [...] While PHP makes it unnecessarily easy to write shitty code it also provides a lot of ways to avoid it. I’ll use this post to show you how ridiculously easy it is to create a template engine in PHP in three easy steps.

He includes the sample code for a "Template" class and shows the combination of exporting variables and output buffering to return the resulting template populated with values. The "__toString" method makes it so that you can just echo out the object and get the results.