They seem rather silly to me. As far as I know, there is no law saying that people have to follow their privacy policies. And even if there was, people could still cheat. Either you do business with (or join sites) that are ethical, or not. You can trust the ethical ones not to share your personal information. The unethical sites, however, have privacy policies that can't be trusted.
Just because a websites says they will protect your privacy doesn't mean they will. In my mind, it is a better idea to make a judgment based on the reputation of the business or website.