The New York Times reports on what amounts to a seismic shift in Census data recording gay couples in the United States. Whereas once people who indicated that they were living in same-sex relationships on the Census were mostly concentrated in the traditional gay meccas, now they're far more spread out. The result is that San Francisco, which registered as third in 1990 for percentage of gay couples has now fallen to number 28. Of course, some gay meccas that are more small town-ish have gone up on the list, indicating that the changes are fairly complex.
That said, there are two major trends going on that are influencing these numbers. One is that more people are coming out as being in a same-sex relationship altogether. I recall during the Census that there was a major push in gay activist circles to talk same-sex couples into outing themselves on the Census, indicating that there was a prior problem of people in romantic same-sex relationships being counted as roommates in the past. The other important thing is as tolerance for homosexuality increases, gay couples can be more free in moving where they want. Just because you're gay doesn't make you a city mouse, but in the past far more gay couples felt they had to stick close to liberal urban centers to avoid discrimination and abuse. Now getting middle-aged and moving to a a slower life in a small town is an option for gay couples, too, and it's not surprising that many are taking it.
One thing I'd be curious to see, but unfortunately isn't recorded by the Census, is how concentrated out-gay singles are in the cities, and if that's changing over time. My sense is that it's probably not changing as rapidly. Moving to a smaller community is a lot easier if you have a partner for both gay and straight people, but at least you know if you're straight, there are straight people to hook up with and date everywhere you go, at least in theory. As Dan Savage repeatedly emphasizes to lonely gay kids who call his show, the fact that gay people are a small minority makes having gay meccas all the more important for someone who's still on the market. I'd be surprised if the urban gay meccas didn't still have the lion's share of single gay people, especially young people starting off their careers and therefore needing a little bit extra support. In fact, the appeal of liberal urban areas for all sorts of people who need extra support systems is well-known, which is why the same cities that attract large gay populations also tend to attract a lot of independent single women who are more interested in building careers than settling down and getting married. Unfortunately, there's no quick and easy way to record data like "gay but single" or "straight female who wants to keep it light for now," so those numbers continue to go unrecorded.