I used to work in the Shangri-la Hotel in Bangkok and think it's unfair to tip the maids if you don't tip the laundry, security, front desk, consierge, etc.
There are to many on this thread, and foreigner in Thailand generally that care too much what the Thais think of them.
I never tip barbers, dentists, or gardeners.
Farang who tip make it hard for the ones who've lived here a long time and understand the culture.
I tipped my caddie 340 baht tip today and didn't even get a thank you.