The Stone Power feat (ToB. p. 32) allows you to voluntarily take a penalty to your attack rolls in order to gain temporary hit points:
When you use an attack action or a full attack action, or you initiate a Stone Dragon strike in melee combat, you can take a penalty of as much as -5 on your attack rolls. This number cannot exceed your base attack bonus. You gain temporary hit points equal to twice the number that you subtract from your attack rolls (to a maximum of+10). These temporary hitpoints last until the beginning of your next turn.
Stone Power is clearly based on the Power Attack feat (it can even be treated as Power Attack for for prerequisites). However, Power attack uses different wording for its attack penalty:
On your action, before making attack rolls for a round, you may choose to subtract a number from all melee attack rolls and add the same number to all melee damage rolls. This number may not exceed your base attack bonus. The penalty on attacks and bonus on damage apply until your next turn.
If you are attacking with a single action (using the Attack or Full Attack action, or initiating a single strike), adjudicating Stone Power is straightforward - the penalty applies to all the attacks that are part of the action.
However, it's possible to attack with more than one action during your turn:
- You could attack with your standard action, then use something like Celerity (PHB2, p. 105) or a Belt of Battle (MIC, p. 73) to get a second standard action and use it to attack again.
- You could have an ability like Shadow Pounce (Unapproachable East, p. 36) or the Sun School feat (CW, p. 112) that allows you to attack when you teleport, intiate a strike with your Standard Action, and then teleport with your move or swift action(s) to make additional attacks.
- You could be something like a Choker or a 9th level Swiftblade that can naturally take multiple standard actions per turn.
In cases like these, does the penalty from Stone Power apply to all your attacks for the round (like Power Attack), or only those that are made as part of the action on which you activated Stone Power?