I lived on Lamma for a year ... it's one of the few areas in HK where you don't have to pay an arm and a leg for a house with a large garden or backyard.
I think people who choose to live on Lamma are people who value having fun more than other mundane things in life (like, you know, making money and work.) It's very easy to meet other fun, out-going people. If you like mountain biking, Lamma is like the mountain biking heaven of HK. I'm a kayaker, and not a few of my old lammarite neighbours were also kayakers who frequently paddled kayaks to pick up groceries or to access the less crowded beaches. On weekends, lots of lamma local ride their bikes to the powerplant beach to launch their yacht or kayaks.
It's also a small community, so people in the area tend to know each other and go out of their way to help each other. I was able to get along quite well with both expats and locals in my neighbourhood (Pak Kok Tsuen). Of course, it helps when your fellow villagers like your dogs
We eventually decided to move mainly because of the transportation ... I worked nightshift at the time and had to take the kai-to on a daily basis, which gets really really expensive. Even if I could catch the last ferry to YSW, I still had to spend 30 minutes hiking in the dark, dodging snakes and all to get back to my house.