I’ve used Action Points in my games for almost 20 years, in addition to 4th edition rules, in my campaign Action Points are a tool for enhancing combat, allowing anyone to make that critical shot or check when it really, really matters. Action points are also a way to draw the players into storytelling. The DM should always require players to justify their use of action points by describing the enhanced action in detail.
Consider the player who 99% of the time just declares, “I attack the monster and roll an 18.” If he wants to use an action point to enhance the roll, the DM is perfectly justified to demand a more colorful description.
What makes this action so spectacular? Does the character distract his foe with a cunning move? Does he score a hit through dumb luck? Does he shift position so the sun is in his enemy’s eyes? If the DM wants to hold the game to a high standard, she could rule that unless the player comes up with a good story, the action point can’t be used at all!
So in addition to the 4th edition rules, Action Points can also be used as a bonus of +1 or 10% to any roll! I’m open to creativity on this, if you come up with an inventive way to use it I’m more than likely to let you.