On the PHP in Action blog, there's a new post looking at a recent library that was posted to support type hinting on scalars. They agree with his choice of subjects, noting that they see type hinting as much more useful on scalars than on objects.
I admit that these judgments are hard to make. I could be wrong, more or less. Type hints are probably useful when code becomes stable enough and at the boundaries between modules. But I still tend to avoid using them until I get an actual bug that might have been prevented by a type hint. Their usefulness is and has to be an empirical question. The purpose of using them has to be catching errors earlier, so if they don't have that effect, there's no point.
He lists three reasons why he had given up on type hinting before, one being the limited usefulness when it came to objects. Applying it to scalars is a different matter, though, and can prevent improper passing of array/scalars when the other is needed.