I think it defeats the purpose of going portable but to each his own.
Me, personally I was given my laptop by my college. I do a lot of computing on the go, and as a designer I really benefit from the 22" widescreen at home for juggling large images and actually using Word without the toolbox in front of my publishing screen..
If you use your laptop on the go, love to take it out and use it around town or travel with it, and you need a serious desktop solution, then why not buy a 150-200$ monitor, 30$ laptop stand and a Kb and mouse? You will get both a desktop and a laptop for around 2-300 bucks more (maybe cheaper depending on your deal). It is far cheaper than even buying a Mac Mini to use as a home computer (and purchasing a monitor I may add). So you can see the relevance, many people can actually use it.
As a student.. I need it. Have you tried to design a 1680x1050 image on a 1280x800 screen? Sucks. With a touchpad sans mouse, sucks even harder. You scroll and scroll. Images take much longer to produce. If you want the best of both worlds, a few hundred bucks isn't a big deal. Go mow some lawns.
If I go to the local coffee shop, I will tug the laptop with me. It's 13" and the current definition of Apple portability computing. You won't get the, "Oh he's bringing his 17" laptop with him, that thing is huge." You can be as nondescript and coy as you like. The most people will give you is longing and admirable stares. Or the occasional Windows fanboy disgruntled stare.
Then I come home, set it on it's stand, plug in the USB splitter, MD2DVi dongle, Power Cord and Speakers. I am desktop computing in less than 30 seconds flat. Personally I rather like it.
