I think T@G is a downloadable application/game, but I agree that everything we know so far, from info, that footage gofreak posted yesterday, to these slides would make for an interesting, all-encompassing Vita OS thread.
Notice how we're supposedly able to switch between Index mode, Live mode, and Game mode by simply "tapping" the PS button, so it seems like the Index mode is the most general/outer layer. Live mode is where the chunk of the OS is, and that's where we get to flick left and right between the suspended apps. As for games, if I remember yesterday's video correctly, the guys asked Sony's rep to go back to the game when he caught them snooping around. I think they said something along the lines of "holding the PS button for ten seconds? that's how I go back to the game, correct?"
Having to "Hold" a button sounds like how suspend a game a la PSPGo, at least to me.