They're fun for the guys who programmed them, they are useful for the users who play them. And vice versa. (Solitaire in Windows for example helps you exercise your mouse control).
Ax comes with some games as well, showcasing some of it's programming techniques.
You'll find them hidden in the AOT under the forms node, just lookup under 'Tutorial'.
An overview:
Horserace (form tutorial_HorseRace)
A simple betting game, showcasing a progress bar and using random numbers.

Memory (form tutorial_Memory)
A very basic memory game, with buttons on a form.

Tetris (form tutorial_Tetris)
An implementation of the arcade hit Tetris. With graphics. And a timeOut implementation. And catching keystrokes with the task method.

During some extra time a couple of years ago, I extended the Tetris game in Ax. I've included some start levels in them. Feel free to download the modified version from my SkyDrive here .
The above games are included in Ax 2009. The older Ax versions had some more built-in fun, like BattleShips,

or Tic Tac Toe.
The people over at Trucos Ax, an Axapta community site in the Spanish language, even have a link up for a Space Invaders game in Ax. Cool! Maybe the gameplay isn't as smooth as you can find in the arcade hall, but this is definitely a solid effort to bring back that old spirit.
Know some more ways to have fun with Ax? Share it in the comments!