High on the list of things your Mac can do that a Windows PC can't is the exceptionally useful FireWire Target Disk Mode. But what is it, why is it cool and how can it help me?
Back in the day, before USB, before Firewire and probably before colour TV (ish) Mac's used a system for connecting to external devices called SCSI (pronounced scuzzy, because it pretty much was). One trick that Macs could pull using SCSI was called SCSI disk mode, which when invoked this turned your Mac into a big external hard drive that generally failed to connect to much because that's what SCSI was like. This neat hard drive trick was transferred over when FireWire debuted, the main differences were that it became known as FireWire Target Disk Mode (FWTDM) and that it actaully worked reliably.
So how do you use it? Simple, just hold the "t" key on the keyboard down when starting your Mac and hold it down until the screen comes on and shows a large FireWire symbol. Your Mac is now in FWTDM. Using a firewire (400 or 800 cable depending on which connector your Mac has) you can now connect your Mac to another Mac (or PC if you want), where it will appear as an external hard drive.
OK, so why do you use it? There are many reasons why FWTDM can be a life saver. If you have a large amount of data to move to or from your Mac but no easy way to network them together (no wired network, file to big for wireless etc) then FWTDM allows you to move data at the full speed of the FireWire connection. Great for dumping movies or other huge files onto your Mac. BUt that's not all. If you need to install a new OS onto your Mac, you could use the install DVD and the optical drive, but what if the optical drive is broken (what a Mac optical drive not working, no way! Well, yes way. Indeed). Connecting your Mac to another Mac via FWTDM means you can use the optical drive from that Mac to install your OS. But better than that, if you have created a disk image of your install DVD on the hard drive of your other Mac, you can install the OS from that, at hard drive speed, rather than optical drive speed. And that's much much faster.
Any other uses? Well, yes. There can be many many reasons why your Mac might start to misbehave, OS faults, permissions problems, hard drive damage. And almost none of them are easily fixed when your hard drive is busy actually running your Mac. Firing up FWTDM and connecting to another Mac will allow Disk Utility to have a better shot at fixing your system issues. The same goes for Disk Warrior, Tech Tool Pro or other utilities. No need to faff about with emergency boot DVD's just connect to another Mac stuffed full of diagnostic tools and check away.
So, FireWire target disk mode. A hidden feature of your Mac that can be either very useful or potentially life saving. Well done Apple.