If I have a character with pounce, leap attack and Power Attack, I can combine a charge attack with a jump and potentially triple the bonus damage granted by power attack. However, pounce allows me to make a full attack after a charge. If I do this, does the bonus granted by Leap Attack count for every subseqeunt attack made this round, or only the one right after my charge?
Leap Attack improves your usage of the Power Attack feat after a jump that meets the qualifications laid out in the feat. Power Attack’s penalties and bonuses last for an entire round, so when you use Power Attack (“On your action, before making attack rolls for a round, you may choose to...”—when you choose to, that’s using Power Attack) after triggering Leap Attack, the larger bonus that you get lasts as long as that usage of Power Attack does (“The penalty on attacks and bonus on damage apply until your next turn”).
In other words, yes, the benefit from Leap Attack applies to all attacks made until your next turn: extra attacks from pounce, attacks of opportunity, whatever.
Also of note: Leap Attack uses the very awkward phrasing “+100% the normal bonus damage from your use of the Power Attack feat.” Because it is adding a certain amount of damage (100% of your Power Attack bonus damage), rather than simply doubling that bonus, it does not count as multiplication for the purposes of 3.5’s weird math. That is, if your normal damage bonus is 2×penalty = +40, Leap Attack adds 100% of that (+40) to get +80, rather than simply doubling which, in this case, would be doubling something already doubled—resulting in 3×penalty = +60 damage total instead of +80.
And then on top of that, if your attack’s damage total is also being multiplied (e.g. with Spirited Charge or whatever), that multiplies the damage bonus according to regular math, not weird D&D math. So if your attack would deal 2× damage, the bonus from the Leap Attack + Power Attack here would be 2×[(2×penalty)+(2×penalty)] = +160.
These numbers get very large very quickly, because multipliers are powerful. Which is exactly why the rules usually have multipliers add together, rather than applying according to the normal rules of mathematics—but then they went and ruined it by printing stuff like this that gets around that rule. The result is the Übercharger.
I wouldn't let players add Leap Attack to all attacks because simple logic tells you that the first attack gets more momentum from the leap all the other that follows don't. Power charge is a similar feat and says "Special: If you would make multiple attacks as part of a charge, this feat only applies to the first one." So Leap Attack should have something like that as well. Leap Attack just have a really horrible description which should be corrected in many ways.