I just got back yesterday from a 3-night stay at the GCH.
Until coming to these boards, I'd never heard of tipping hotel maids. I did grow up in the 60s and I did have conscientious parents who tried to instill manners and breeding, but tipping hotel maids was never something my family knew about, apparently.
I began feeling guilty after reading these threads a few years ago and started trying it out. For the past 3 years I've tipped. In all but one case, my service was nothing special and often worse after tipping. No idea why that would be so. This trip, I decided after I'd left $3 the first day (I was with my sis and she left an additional $3) that I was no longer going to tip because although our room was clean, there were some issues (like 1 towel, no shampoo, etc). Our room was fine the next 2 days but it didn't change my mind.
My decision is that tipping housekeeping is not something I will do anymore unless they do something really outstanding that I want to recognize. I don't think it should be up to the guests to subsidize employee's pay, but tipping for outstanding service is always a nice gesture.