Mark Brady has a recent post he's worked up that looks at a feature in the upcoming PHP 5.3 version - closures.

According to object-oriented programming expert Martin Fowler, closures are defined as a block of code that can be passed to a function. [...] PHP's upcoming syntax for closures is shaping up to be comparable to the C# 2.0 implementation.

He includes two code examples to compare the two language's methods - one for C# and the other for PHP - that divides the input by a denominator and returns a true or false depending on the result. For more information on closures, see this proposal on the PHP.net wiki.