http://www.pcworld.com/article/id,134275-c,gameconsoles/article.html
MS was already asked this and they basically responded saying july is a weird time to drop the price. Now that PS3's price-drop is for a limited time, I doubt they'll bother until this holiday season. Maybe around September when Halo and the 65nm chips ship.
They have no reason for a price drop right now. I doubt there will be one until well into next year. But if they do Sony would absolutely have to bring the price drop back to the PS3.