Harvardx even mentioned they registered because they felt this thread was informative and they learned something from it. And I'd bet there are many who are reading but not posting that feel the same way.
I'm one of those that have been reading this posting and haven't responded until now. I've never tipped housekeeping because I really didn't think about it. But after reading all these posts, I have printed out some envelopes to take with me on our trip in Oct. so I can tip housekeeping. I can't believe I never thought of tipping housekeeping, but you're right, their salary is quite low and they deserve to be tipped due to the amount of work they do. They probably work harder than 80% of the population. I do tip my hairdresser because I know that most of the money goes back to the business. I even tip the pizza delivery guy.