In this recent post to his blog Michael Kimsal asked about the usefulness of the __get and __set magic methods and the sort of code he usually sees along with it.
For a long time I've held that __get and __set in PHP were not all that hot - mostly because it's solely error handling. There's no way to deal invoke __get or __set behaviour for properties that are defined on a class. [...] For those who insist on using __get/__set, I *typically* see this [messyy] sort of style code. The effect is to cram a bunch of unrelated code in to the __get/__set overloading methods.
He suggests an alternative to the "cram it all in __get" approach - callbacks to other methods in the class to handle the different variable possibilities. In the comments there's other suggestions on how to get the same job done differently - mapping property values with __call, valid uses for getters/setters and a pointer to an internals discussion RFC about this same thing.