It's amazing how many people are missing the point - it's not about playing on a tiny 5" screen, although that is something you can do - it's the idea that if you don't want to sit in front of your pc, you don't have to, and it can go on to a tv etc.
My sofa is far more comfortable than my desk chair, even if it is a nice leather executive one. My cinema surround setup is worth more than my car. Generally speaking, a gaming 'experience' is much better on a larger more immersive screen, more comfortable setting, and better sound.
What this actually boils down to is 1) whether or not lag is an issue and 2) the old joypad vs mouse/kb debate. Both of which vary person to person.
There has been software around for a while that loads up a game on your main computer, streams it over a network to a laptop for example, and let's you play the full power of your pc on something that might otherwise not be able to. I think the concept is good, and it's all about pulling off lag/visual quality.