You'll get a lot of variety of answers on this question. Some don't tip at all, saying that housekeeping doesn't even get to keep their tips. I don't think anyone has ever been able to verify that with DVD management.
Others feel that since T&T is so minimal, they provide a minimal tip (or none for that day).
Personally, I share wdwnut's philosophy....that's about what we will tip for a 1BR.