The interesting thing is that he's using it to replace his Mac Pro. Most tech professionals have a primary machine (often a desktop) and a secondary (usually a laptop). After living with this setup for some time, Shawn noticed that the laptop had become his main machine:
"I don't need the Mac Pro. The loss in horsepower is negligible for what I do, and the gain in simplicity cannot be expressed with words. I'm selling the tower and going back to being a one-computer consumer, and connoisseur of fine laptops."
The same thing eventually happened to me. My MacBook Pro is the machine I use most often, and my iMac is the machine I use to sync my iPhone, make iTunes purchases and upload photos. Other than that, it pretty much just sits around.
Shawn goes on to describe setup, migration of his older data and (much, much) more. The whole thing is written in Shawn's comprehensive and readable style. Check it out.