It really depends on the amount of powder and the kind of powder. I don't use it myself but I've handled a friend's deck which was really overpowdered as he called it.. and I'm pretty sure that that deck still feels the same as it did back then.. a year ago.
The bad thing is that using the cards more might actually have the powder work the cards more too. I'd suggest you to stop using the deck, getting a soft brush over both sides of every single card and making sure the surface you do it on is clean once you are done cleaning a card's side.
Hope that helps.