(Not relevant to most of you since for the most part you aren't Canadian, but tales of Government Fail are usually universally appreciated.)
The tax deadline for paying taxes in Canada is usually April 30th, unless that day is on a weekend or statutory holiday, when the deadline is bumped to the next following business day, making the tax deadline May 2nd this year since April 30th was a Saturday. Payments and returns received or postmarked on or before May 2nd would be 'on time' and incur no interest or penalties.
We knew that. The Post Office knew that. The news media knew that. Canada Revenue's website and telephone operators knew that. You know who didn't know that?
The Revenue Canada computer system.
According to the beleaguered Revenue Canada call centre person I talked to, the computer system (or something relating to the computer system, he wasn't too clear on details) did not get notified of the deadline change, and anyone paying their taxes after April 30th was flagged as late and charged interest. They are only now starting to discover this error as the notices to pay interest are being received by taxpayers, and they are calling Canada Revenue. Hundreds and thousands of them.
So, the semi-official word, direct from the Revenue Canada Call Centre Operator Guy is: 'If you sent in your payment postmarked May 2nd, ignore the interest, we're fixing it. If you're still getting letters about it in a month, call in then and we'll fix you individually'.
I'm hoping they'll do a proper news release or something soon, because it's gonna be nuts and actual details from the source would be nice. :-P