Do You Have To Give 30 Days Notice To Vacate An Apartment You Are Renting Month To Month Without A Lease By The First Of The Month?

I am on an unsigned month to month rental agreement with my landlord. I gave a 30 day written notice to vacate on 11/6/07 and now my landlord says that I can only give my 30 day notice on the 1st of the month, and that because I didn't give my written notice on the 1st, I have to pay all of December's rent, not just the prorated 6 days. They let us pay a prorated amount to move in early, why not to move out late? Is this legal?