Felix Geisendorfer has a great functionality note that CakePHP users might want to check out. It's related to the Set class and how it handles nested arrays.
So far this has been a little dark spot for me in the core and from my previous quick looks at the class I've never been quite able to figure out what it's exact purpose was. Until now all I knew was "well it's probably some fancy array manipulation code that is somewhat obfuscated and undocumented". Oh boy, I wish I had spent more time on this earlier. It's probably one of coolest new features in 1.2 and nobody realizes it.
He starts with a simple example of how the class works with a nested array of user information. Normally, you'd loop through the array and append the values you'd need to another array (like the user's name), but with Set, it's as simple as calling the static "extract" method with the "path" to what you want out of the array. A simple one-line replacement for a (normally) three to four line bit of code.
He gives a few other examples using this same user information, grabbing various results and includes one at the end that is very nice indeed - pulling in an XML document, running it through a simple xmltoArray function and pulling out the titles in a few easy lines.