Timothy Boronczyk has written up a new blog post about two of the features he's most excited about in the upcoming PHP 5.3 release - anonymous functions and closures.

As of version 5.3, PHP will offer better support for anonymous functions and a new syntax which supports closures. [...] Anonymous functions are functions that are defined without being bound to a proper name. Typically, anonymous functions are used only a limited number of times and for a specific purpose; you could think of them as "throw-away" functions if you'd like.

He includes some code examples showing how the anonymous functions can replace the current create_function method and how closures can effectively import variable values into the current scope just like they were passed in.