I'm a little late getting to this, but the trend is long-term and may not be fully established yet. Alan Ehrenhalt of Governing magazine had a fascinating article in the New Republic about a month or more ago. It argued, using Chicago as the first example, that it's just possible to discern a trend that rather reverses the U.S. urban pattern of the last half century or more. With suburbanization, we saw middle-class people move out of central cities (white flight, some called it) and the central cities becoming dominated by the poor and minorities. Ehrenhalt sees a pattern that resembles cities in Europe -- the affluent moving back into the central cities (gentrification squared), and the poor and minorities populating the suburbs, which works because that's where many of the blue-collar jobs are anymore. Deindustrialized cities become more attractive to affluent people, and something like the ideal of a lively urban life becomes more likely.
The trend seems most marked in Atlanta, and although Ehrenhalt cautions that the numbers are still relatively small, he thinks he sees a pattern. Maybe Jane Jacobs' ideal of cities that are really alive and people-friendly will happen eventually, years after her death.
I don't know. Urban patterns seem to happen in cycles as neighborhoods deteriorate and are gentrified and back again. But it would be interesting if cities became more vital at their centers. Even aside from the fact that I probably couldn't afford them, I'm not sure how tempted I would be. Maybe it's age, but a small town works nicely for me so long as I have plenty of bookshelves and access to the Internet.