It is alomst all perfect in Lamma, except those soaring views of huge power plant near Yung Shue Wan from many angles. Therefore I'd say you preferably start your island trail in Yung Shue Wan into Sok Kwu Wan direction rather than vice versa - because if you walk this direction you'll have the view of plant mostly behind your back once you have surpassed it. But you need to think about this before you take ferry from Central, because it depends which one you take.
Other than that, after strong rains you're not advised to swim in the sea for three days at Hung Shing Yeh beach (that nice, sandy one indeed) because water becomes more polluted. Maybe from that plant.
Anyways, it's just so huge and distincitve and... contrasty... that construction here that it's worth to be warned in advance. Anyways, focus on nice things on Lamma although you cannot ignore some aspects.
I've just come back from Lamma island (18/09/2011) and I have had some symptoms of food poisoning. Although it's too early to be sure which kind of food poisoning I have, I suspect it happened in Tai Yuen Seafood Restaurant, where I had only a small crab, the only sea food I had in many days. The restaurant was full of locals and the fish was displayed and looked great, I might have been unlucky, but there might be some problems in the water where they caught the crabs.