I wouldn't add a day to the week, I'd REMOVE two to have a 5 day week.
Mondays and Wednesdays can go to hell, So work Tuesday, Thursday and Friday; then Saturday and Sunday off.
The genius thing is there are then a set number of weeks per year, 73 in a 365 day year... and leap years are celebrated by having a two day new Year celebration; January 1.1st then January 1.2st so every leap you have ONE HELL OF A PARTY!
Actually, fuck months, they make no damn sense, they are arbitrary anyways. The only constant is is take 365 (and a bit) times as long for the earth to orbit the sun as it takes for the earth to rotate on it's axis.
Months should follow the lunar phases only, dates should just be defined by Year and then the Day within the year (so today's date would be 2010-196). Yeah, I know the Lunar phases go out of sync as they oscillate every 29.5 days but we can have leap months then every few years. So people can still say "I was born in January" or whatever but moon's phases will actually mean something.