Post Offices Closed on Columbus Day? Columbus Day 2012
It's Columbus Day: all public schools and public offices are closed. This means post offices. Post offices are closed on Columbus Day. They've always been closed on Columbus Day. They likely will continue to be closed on Columbus Day. So if you're mailing that last-minute credit card bill, it'll be late.
Meanwhile, the US Post Office website is choking on extra traffic (not that it ever works too well, but hey). Even when you eventually load the page, you'll find it useless, as the USPS does not have an easy-to-find list of its own closures.