I used to play handheld gaming devices while growing up, as they were a great way to occupy my time during long car rides; when I became the driver, the need entertain myself on the long journeys ended, and at that point I stopped playing the handheld systems.
Although I have not played any of the newer handhelds (with the exception of borrowing my brother's DS from time to time), I find some of the functions to look very...eh, not comfortable to operate. For those times that I want to play a game, I would much prefer just to sit down in front of a big screen with controller in hand, as it just provides a better experience when not on the go.