Important: The Tax Cuts and Jobs Act of 2017 repealed the option to recharacterize Roth conversions, for Roth conversions done after 2017. As such, only regular contributions to traditional IRAs and Roth IRAs may now be recharacterized.
When a Roth Conversion is recharacterized, there are certain additional steps that might be required. However, these can be done afterwards. The most important step now is to get the recharacterization completed by close of business today- October 17,. This means ensuring that the amount is moved from the Roth IRA to a traditional IRA (or vice versa if a contribution is being recharacterized from a traditional IRA to a Roth IRA).
If the conversion (or IRA contribution- Roth or Traditional IRA) has not yet been processed, contact the IRA custodian now. The first step in getting a conversion or IRA contribution recharacterized is to have the IRA custodian move the amount to the receiving IRA.  If this step is not completed by the deadline, then any other step is inapplicable.
After the recharacterization has been completed, it must be reported to the IRS. This reporting may include an amended tax return (Form 1040X), IRS Form 8606 and explanatory notes. However, this can be done later as individuals generally have at least two years from the date any income tax was paid for the year to file an amended tax return.
The Deadline is October 31 for some: Taxpayers who live in areas affected by Hurricane Irene have until October 31 to complete their 2010 recharacterizations. Information about this extension from the IRS is available here http://www.irs.gov/newsroom/article/0,,id=246780,00.html
 The deadline is usually October 15, but it is extended to the next business day because October 15 fell on a weekend.
 Only individuals who filed by April 18 have this deadline. For individuals who did not file by April 18, the deadline was April 18.
 A Roth conversion would be recharacterized to a traditional IRA. An IRA participant contribution would be recharacterized from a traditional IRA to a Roth IRA or vice versa.