Didn't Nolan make The Prestige before he started casting and production on The Dark Knight anyways? I'm sure that he would want at least a year break before going back at it.
Yes, he made The Prestige
between Batman Begins
and The Dark Knight
. Another three-year break between Batman films should be sufficient for him to recharge, maybe make another non-Batman film in the meantime, and then deliver the next sequel. All things being equal, summer 2011 is highly likely to see next, and likely final, Nolan Batman film.