You have until October 17, 2011 (because October 15, 2011, is a Saturday), to re-characterize your 2010 rollover or conversion to a Roth IRA if you file your 2010 tax return on time, including any extensions, and regardless of whether you requested an extension to file your 2010 tax return.
FORBES: Before you get out the checkbook, second thoughts on your Roth IRA conversion...