Reasons against

Please add your comments

The system would be too complicated and costly to implement
(Not really, you would give everyone plenty of advanced notice to update computers and digital watches, mobile phones and such)

When would my birthday be in the new Calendar?
(you could calculate the day of the year and then fix it to the new calendar, and it would always be on the same day of the week :)

You would have to change everyones passports and legal documents!
(Not neccessary, you could refer to dates as OC [Old Calendar] and NC [new Calendar], so if my birthday is 25 Feb OC then that would be the 56th day of the year and that would make it 28 Feb NC)

Who would decide what to call the 13th month?
(Oncember perhaps?)

Financial Quarters?
(first Quarter would be exactly 3 months and 1 week, second quarter after 6 months and 2 weeks and third 9 months and 3 weeks, the number of weeks tells you which quarter :)