The maids' quotes at the end of this article are quite disturbing, though I've personally never heard of any similar stories. All the maids I've seen (working for family, friends and colleagues) seem quite happy, and some have stayed with their employers for a long time.
I was quite surprised to hear of HRW's report, as cases of maid abuse do get reported in the local papers, with their employers usually punished by the law. You could say it's just the tip of the iceberg, but surely the right message does get sent out when each case is reported. I recall an article in the Straits Times where model employers were featured with their maids. It was touching to hear of how a family sent their maid for classes so she could improve her career prospects.
Also, it's difficult to legislate on things which happen in the confines of a home, even if protection is extended to this group of workers. It's different from an employee in a company who files a complaint against his employer for abuse or non-payment of wages. The employee doesn't have to live with his boss, nor depend on him for food, shelter and safety.
Based on your personal experience, what do you think about the treatment of maids in Singapore?