My accountant dropped off my tax returns yesterday evening since calendar-year S corporations like mine need to have their 2007 federal income tax returns filed by today.
If your tax return isn’t ready yet just mail in IRS Form 7004 to apply for a 6-month filing extension. I’m cutting it close, down to the last minute; but as long as it’s postmarked 3/17 I should be fine.
If you have a calendar-year C corporation, the same deadline applies.