The IRS “safe harbor” for avoiding penalties is as follows: No penalty is owed if either (a) regular withholdings cover 90% of the actual tax liability; or (b) quarterly payments and regular withholdings cover 110% of last year’s tax liability.

2009 Safe Harbor as noted on the IRS website…
http://www.irs.gov/publications/p17/ch04.html

Estimated tax safe harbor for higher income taxpayers. If your adjusted gross income was more than $150,000 ($75,000 if you are married filing a separate return), you will have to deposit the smaller of 90% of your expected tax for 2009 or 110% of the tax shown on your 2008 return to avoid an estimated tax penalty.

The far majority of people interested in an extension do owe taxes and this is a huge misconception upon people that walk into our offices.

Filing the extension will help avoid a minimum fee, however it is almost always better (if you can) to put in the work now to get them filed!

John

Just read the article on financial blogging that featured your site. Good luck with the online radio show!

John