safe harbor:
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 must deposit the smaller of 90% of your expected tax for 2010 or 110% of the tax shown on your 2009 return to avoid an estimated tax penalty."
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 must deposit the smaller of 90% of your expected tax for 2010 or 110% of the tax shown on your 2009 return to avoid an estimated tax penalty."
