I also want to agree with jgsugden's analysis. Very few people optimize their use of power attack because it is too hard to have all the relevant data on hand. It takes a few rounds to ping the creatures AC. Depending on your campaign, that could mean the monster is already dead, or so close that the power attack won't be making the difference. I have done spreadsheets to optimize my power attack choices given the foes AC and my specific attack routine. It tends to payoff for me because the monsters that I fight in my campaigns at home have lots of hp and come in mulitples (so after the AC of one is pinged, I know how much to power attack for during the rest of the combat, adjusted for various bonuses like flanking/charging, etc.) Anyway, the feat is capable of being very good, but it only gets gross in very specific circumstances, in the hands of a player who puts a lot of effort into maximization (in other words, a geek like me).