On the php|architect site there's a recent post that splits apart the singletons versus static methods debate that seems to com up every once and a while with a better suggestion - dependency injection.

Much more important than performance is the fact that both static methods and singletons suffer from major drawbacks. When it comes to deciding between the two, you might forgo the benchmark comparison and choose the third-party candidate: dependency injection.

He mentions the "dark side" of both static methods and singletons and how dependency injection can help rid your code of both. Instead of focusing just on the benchmark numbers, DI helps you keep your code more well-structured and "smarter" by scoping things to where they need to be and making them easier to test.