[DaFranker]

Inverted Y (vertical axis, i.e. up/down view) is a very popular setting for simulation games and FPS games on PC. It's popular enough that games with >100k players will get bad press and >20 forum complaints (even when the forum is hard to find!) over it, and many more than this will simply not play/buy the game.

In other genres / types of games, especially where you don't control exclusively one character / vehicle from a fixed first/third person viewpoint, it is drastically less common.