I have been using Mac OSX since last few months, and its fun to explore things which apple do. Apple in 2004 introduced XGrid, which allows you to utilize the resources of different Mac OS in your network and gain a considerable performance boost. Here is a great article, talking about How to Turn Your Macs into a Super Computer
The thing which immediately comes to my mind is, whether we can use this in password cracking. I could not find any mention of this on John-the-ripper website. A few emails discussing this could be read here