The IRS warns that rush to meet the deadline can cause errors, often very simple ones such as neglecting to sign the return or bungling the Social Security number.
H&R Block chief executive Mark Ernst said there are also more costly mistakes, including opting for the standard deduction if you can itemize or failing to pay the complicated alternative minimum tax, an extra tax that some people with a lot of deductions are required to pay.
Dave Cohen of CBS radio affiliate WWL-AM asked last-minute filers outside an H&R Block office in New Orleans why they waited.
"It's just something I've fought all my life."
"That's the deadline, but if you owe money, you wait until the last minute."
"I'm a chronic procrastinator. That's all there is to it. No excuse."
"I'm a procrastinator and because it's fun."
"I can use that money. Sometimes, I need that money. The government, they got plenty of money."
"I was on vacation, and then all of sudden it's like BAM! 'Got to do it.'"
The Postal Service was gearing up for an onslaught of late mailers, with longer hours at many post offices and some stunts to mark Tax Day:
A postal worker was being stationed at the Fort Wayne, Ind., Coliseum to accept tax returns before that evening's "Disney On Ice" show. The first 50 characters handing in their returns there were to receive backstage passes to meet the show's characters.
There will be a mobile post office at the Erie, Pa., Sea Wolves home opener to accept tax returns, and a junior orchestra will play at the main post office.
The Arlington, Va., community of Clarendon was holding its annual Tax Blues festival, music, dancing, and food, right next to the post office.
At the Mansfield, Ohio, post office, which will remain open until midnight, customers were being offered hot dogs, popcorn, health screenings and even stress massages.
A local radio station was sponsoring a dunk tank with an IRS agent in the cold seat at the San Mateo, Calif., post office.
Taxpayers looking for a post office with extended hours can call 1-800-ASK-USPS, then use the USPS Web site, www.usps.gov, to find the location of that office. The site even provides maps.
But not as many post offices were staying open until midnight as in previous years, and not as many post offices will have IRS agents available to help last-minute filers — possibly a reflection of the growing use of electronic filing.
CBS News Correspondent Dan Raviv reports the IRS estimates that the average time to gather all your records and forms, and fill them out, if you itemize deductions is 28 hours and 30 minutes. That's 42 minutes more than it took last year, and more time than is left now.
However, if you need more time, you can always get a four-month extension from the IRS. But that only buys you more time to file your return. Any money that's owed is still due now.