I'm not sure how I feel about handheld gaming. Not a lot of time for it in my life, using a handheld console while commuting is just tempting fate. Even in more secure public transportation like a bus, I get carsick. I guess it would be most useful on long airplane rides?
I bought a Gameboy Advance back then for the games (mainly Pokemon), not because I could bring it everywhere I went. This Deck thing doesn't have any exclusives, or even games that were developed with its capabilities in mind, so I have a feeling this will end up just as much of a gimmick as the Steam Machines. And even then, I don't trust Valve one bit to sustain this in the long run.