There's an article in Sunday's edition of the Chicago Tribune about helping Retired Urban People (aka 'Ruppies') adjust to life downtown living after years of suburban living.
The interesting thing is that I've witnessed this trend firsthand. Several folks who live in my condo building are clearly retirees. Last year, I got to know one guy on my floor who used to ride his bike to work. We chatted about the pros and cons of public transportation vs. biking and/or walking. And then one day, he told me that he was moving out because his parents were moving in. Apparently, they'd finally decided to kick him and his brother out of their 'retirement home'.
Personally, I can't see my parents or any one of their friends retiring and moving into the city. They would be way too irritated by the noise and inconveniences of downtown living. But having acquired a taste for urban living, I might consider it.