Superuseless Superpowers is a blog by an anonymous cartoonist who has taken up the task of chronicling the most useless superpowers. Above is his picture of the superpower 13th Bullet Proof -- being completely safe from 1 out of 13 bullets shot at you.
I gotta say that the most useless superpower I ever saw was in the old Palladium role-playing game Heroes Unlimited. It was clock manipulation: the ability to stop or change the time on a clock through psychic powers. I'll take invisibility or wingless flight over that any day.