To the posters who say adult children in full time work shouldn't pay housekeeping, or should have been taught the value of money earlier, I say this.
My DS was taught about the value of money. We struggled and went without alot of things when he was younger because we were so poor. He learnt to save very young and was exceptionally good with money. He knew the value of money, it took him long enough to save anywhere near enough to buy anything he wanted.
I never ever concerned myself with worrying about DS and his finances. He used to say that overdrafts were for the reckless and should only ever be used in emergencies, since it was clearly the banks money. He appreciated every penny, has worked solidly since he was 16, as well as going to college full time.
He moved in with my DM 6 months after he started his first job, when he was 16 and a half and from that moment on, he no longer contributed in any way shape or form to the household. DM has never asked him for a penny. She does everything for him. He is not expected to lift a finger, and does not even clean his own room.
He went from contributing to most household chores, and saving his money for the things he wanted, to doing nothing in the house, and keeping every penny to himself.
Has this made him richer? Has he saved more? He pays nothing and spent his entire childhood being taught by example as well as verbalisation that money was valuable, not to be squandered.
Has it heck!!!!
DS very quickly forgot the value of money, since he's getting everything for free. He has no respect for DM, he has no respect for anything material, or any appreciation of what others sacrifice for him.
He spends every penny of his money on drinking, smoking, going out and having a good time. In fact, with all the money he has spent on drink, he has gained something.....a liver problem, to go with the stroke he had whilst he was at work last year. 
He has given up on driving lessons, is up to his eyeballs in debt with the bank, and after so long of this, resents being asked to do anything. He believes that it is his right to live for free whilst he remains living with a family member.
Has my mother done him any favours? Absolutely not.
Does my mother feel unappreciated and used? Yes
So if you want your DC's to be selfish and believe the world owes them a roof and free food, don't make them pay a penny, but don't expect them to thank you for it afterwards. Ime I have never known an adult DC to thank their parent for being a mug.
I have known many DC to thank their parents and appreciate their parents teaching them the cost of living though.