On the Setfive site there's a recent post from Ashish Datta about some thoughts around array functions and closures for callback methods.

The other day, I was hacking away on the PHP backend for the “Startup Institute” visualization and I realized it was going to need a good deal of array manipulation. Figuring it was as good a time as any, I decided to try and leverage PHP 5.3+ new closures along with the array_* functions to manipulate the arrays. I’m not well versed with functional programming but I’ve used Underscore.js’s array/collection functions so this is mostly in comparison to that.

He gives a sample data set he's pulling from - basic user data - and goes through a few different actions that can be taken on the data (with code examples for each): sorting, mapping and filtering. He shows the use of closures as the callback methods instead of defining them separately and passing in their names.