I'm mastering a star wars campaign (revised core book) and thought to implement xp-awards for good roleplaying, backstory, etc.
The problem is that in star wars, any difference in experience doesn't disappear with time, but increases, causing the players to be of different levels a fair deal of the time.
Furthermore, promoting a certain player for his roleplaying efforts will (in my experience) annoy the others, or (worse still) cause them to enter some sort of competition at the table. Yet for me, D&D is about co-operation between players and not struggle. I do not want to compare the players abilities.
The way I went is instead of giving xp, I award force points more often than suggested. I try to give them whenever something meets the requirements (e.g. a clever idea that propels the story forward or helps the party to achieve in accordance with their moral outlook) and not giving them to whoever does something best. That means that either you get a force point, or you don't. No varying amount as often the case with xp-awards.
Force points seem better suited for this kind of reward because they are an expendable resource and players spend them at varying rates. So you're not slapped in the face after each session by the fact that you still have the least xp of all players. In addition, if someone spends a force point, it is usually to save his ass, something that benefits the group as much as himself. Having more force points doesn't make one character superior to another the way a different level count does.
Seeing that 3.x D&D doesn't have action points, I'd shift the benefit for background creation and roleplaying to the equipment side, as already mentioned by some, awarding masterwork or minor wondrous items. Maybe you make friends with a wandering merchant and he gives you a talisman to protect you on your journeys, etc. While this technically gives someone the edge other someone else who doesn't have that item, it aids him only in one or two categories, often improving something he is already specialized in and where there is no competition over who gets to do something.