Should you write a "thank you" letter to an employer following an interview?

I don’t do them (and it has never stopped me from getting the job). I find the whole idea of it a bit false, a bit of a suck-up, a bit “I really want you to think I am a nice polite person, please hire me”. If I were hiring, it would turn me off.

Some people say they are a must though; that they work; or say as employers they really do appreciate them. What would be your preference?