After hearing Stefan Priebsch's talk at this year's Dutch PHP Conference, something occurred to Derick Rethans - there was a small sort of issue with using namespaces and possible future PHP's own namespace.
One of the things that came up is the conflicts that can arise with internal classes. In PHP 5.3 this would alias the class Interval in the namespace PEAR::Date to the class Interval. For now, this code would work just fine. However, if PHP would introduce a class "Interval" at some point in the future (and PHP can do this as it owns the global namespace) then the above code would suddenly stop working
He offers a simple solution that can prevent this sort of conflict for the future - defining your "use" and then creating a new instance of the namespace into a variable instead of just an "as".