Eric Hogue has a recent post to his blog looking at one of the more tricky aspects of the latest versions of PHP (the 5.3.x series) - late static binding. In a nutshell, late static binding (LSB) lets static classes and methods work more correctly than before. Eric gets into a bit more detail than that:

It came out almost 2 years ago, but it to me that many programmers around me have no idea about it. Myself, I have learned about it around 6 months ago. The PHP documentation defines late static binding as a way to "reference the called class in a context of static inheritance." This definition didn't really help me the first time I read it. Fortunately, there are more explanations in the documentation, and there are good examples. If you haven't, you should read it.

To clarify, he includes a code snippet showing the use of the "static" keyword to correctly reference a static method. He also includes in interesting bit about when's a good time to use it.