Sean hits on the fundamental problem, from a GCA perspective, of the points/flexi membership schemes that are designed to attract the 10-20 rounds a year players, which is that they are not really available anywhere you'd really want to play.
Simon's question about attracting twenty and thirtysomethings is a real one, and it extends into the forties for many as well. The issue is social mobility. With people moving around more, the great club atmosphere where you can mooch up on spec and just pick up a game is really hard to come by. I've told this story before, but my at Dad's club in Yorkshire there are a bunch of guys in their 50s and 60s who have known each other for thirty or more years, and you really don't need to ring round to arrange a game - you know there'll be four or five minimum gathering at the club at half eight on a Saturday morning, and increasingly during the week too, as more of them retire.
That doesn't happen so much nowadays. Don't cry for me, Argentina, because I have plenty of other sources of games, but I have no real golfing social circle locally, and thus it is hard, verging on impossible, for me to get value from a club membership at home. I've been toying with country memberships in a couple of locations, because I reckon I could get the ten or fifteen rounds out of them that would make them worthwhile (one would be Burnham as my cousin lives only a couple of miles from the club and is on the verge of retiring from cricket).