Today I grabed the Mad Catz thumb stylus pack (includes thumb stylus, and three regular replacement styli). I realy wanted to use my thumb, but I hated the angle limitations on the thumb strap that comes with the ds, my thumb tip would often touch the screen sending the acuracy off. With the Mad Catz one, wow, Metroid first hunt was so much more fun, even with the stylus it never felt this close to mouse control.
Its not quite for every stylus game, like it might not work so well on games like pac n roll, because I tried the morph ball mini game with it, and it threw my game way off. However, for games like mario 64 and FPS', this may be *the* way to play.