It's been just over a year since I got my PPL and in that time I have been renting from the club I learnt at. Mostly because of the weather I have done far fewer hours than I intended to, and because of the need to get the aeroplane back for the next booking, I have only flown fairly locally. Someone said that many PPLs consider 2 hours to be a long flight - well it is when the club want their aeroplane back in one hour! Fortunately my club seem happy for me to take an aeroplane away for 4 hours - I haven't asked for a whole day yet!
It would be very easy for me to give up flying, except that I have grand plans to buy a share, get an IMC (and IR eventually) and use the aircraft as a means of transport rather than an expensive way to buy a cup of tea! I'm not in a position to buy a share just yet, so for this year I've set myself goals that I can achieve while still renting - flying different types, fly a minimum number of hours, visit a minimum number of airfields etc. As has been mentioned by a few posters, I think the lack of goals post PPL is a real problem.
The social scene at my club is pretty much non-existent, but I have found the instructors very helpful and they do seem to take an interest even though I've got my PPL. If the weather looks a bit iffy, they'll quite happily talk about what is was like when they were up 15 minutes ago etc, and on a number of occasions when I've wanted to go up but the crosswind has been really strong, they've come up with me for a few circuits for free. They've actually been much better since I got the PPL then they were when I was learning!
I'm interested in the comments that girls are ignored when they turn up at flying clubs. In my experience people at flying clubs are very keen to talk to the "rare breed" when I turn up. It always makes me rather self-conscious about my parking when everyone stops and looks at me when I taxi in! I have never found the flying environment to be at all sexist - but then I work in a male dominated industry, so maybe having been in that environment for years, my attitude doesn't encourage sexism.
In short, I think letting your PPL lapse is a personal thing, and there's probably not a lot clubs can do to prevent it. You either really want to fly, or you don't. I don't think nicer machines etc would fundamentally change that. If you don't have goals or really love being in the air, then it's an expensive and time-consuming hobby, which is dependant on good planning and reasonable weather and, as such, requires a level of commitment that most other pastimes don't.