Daniel Cousineau has posted briefly about a relatively new addition to the feature set of the upcoming PHP 5.3 release - closures.
I'm fairly excited because as of only a week or so ago I found the closures rfc, and not only did I find that the rfc has a working patch, apparently it's already in PHP 5.3. You see, apparently it's not good enough that we get name spaces and late static binding, oh no, we get closures too!
He downloaded a snapshot and gave it a try - code examples are included with his post.