The idea makes great sense, and being a desktop computer (even though it’s small enough to take with you…) makes it a logical upgrade. The writer gives benchmarks of his tests to show the actual speed gains. And depending on the extra parts you may have lying around, you could do this for anywhere from about $50-$200.
I haven’t looked too closely at the slew of 3rd party Mac Mini extenders that offer external hard drives, but it would make sense that they would (or should) be connecting via firewire to enhance the speed of the available hard drive.
I won’t ramble on anymore about this idea. Go read the actual article and see for yourself.