Characters in Stealth mode move at 50% of their total current speed.
Hostile actions take the user out of stealth mode immediately. There are rare instances where one would reasonably construe an action as hostile but, due to game mechanics, it is not treated as such (e.g. damage from a Hellfire Warlock's Hellfire shield).
Once stealth mode is ended for any reason, it cannot be re-entered for 6 real-time seconds of game-play.
True seeing and similar spells will not detect a player in stealth mode, while spot and listen may do so (with respect to movement and noise generated while moving).
Elves (via their Keen Sense feat) are granted 6 checks per round to reveal opponents in stealth mode, while all other races make one check per round.