I think an even better example are 'leader-type' feats:As an example, here is a fake feat: If a player with this fake feat were able to hit twice during a turn, such as with an action point or a power like twin strike, the feat's effect would not stack with itself. It could, however, still stack with different untyped bonuses to AC granted by different feats.
e.g. "Inspiring Attacker: Whenever you hit with an attack power, your allies gain a +1 bonus to attack rolls until the end of your next turn."
Now, if several party members had this feat its effect would not stack.
IIRC, the main reason for introducing this rule update was because of the potential abuse of certain warlord feats/powers in groups with multiple warlords.