iFixit, the folks who specialize in taking apart electronics and gadgets and writing repair guides have recently posted a story explaining a new screw that Apple's devices are using. Screwdrivers for the type of screw they are using is less-readily available than the previous one, which was just a Phillips head.
The new screw is a Pentalobe, and is much more difficult to find the tool for. Currently, it's placed on the outside case of the iPhone and the MacBook Air as well as covering the battery in the MacBook Pro, according to iFixit. iPhones taken into the Apple Store for repair are said to have their standard Phillips head screws replaced by the Pentalobe screws.
It's all a bummer if you do self-repairs, but those who send their computers in for repair anyway may not be to bothered by it. Still, iFixit has a kit put together on their website for replacing the screws if you're interested. First, you can read more specifics about the new screw on their blog.