I have always just left $2 or $3 a day....even though there are 5 of us, we (I!) leave the room immaculate....I cannot stand a messy hotel room!
But, I just read "Nickel and Dimed" where a writer went "undercover" and worked a succession of low-wage jobs (diner waitress, Merry Maids and
WalMart). I think from now on, I'll tip $5 a day.
I will say that before I frequented this board, I had never heard of tipping housekeeping.
Note to all "new" tippers: It may sound compulsive, but it is really a good idea to prepare your tip envelopes before you leave for your trip (even if you DON'T decorate them!). Mornings can be such a rush that it's just adds a layer of stress to be digging for $1s or $5s for the tip.