Many farmers elected in 2010 to convert their regular IRA to a Roth and either pay the tax in 2010 or spread it out over 2011 and 2012. However, if a farmer had elected to get an extension until October 15, 2011, they have until that date to "unwind" the conversion and treat it as if it never happened.
The primary reason for considering this is the drop in stock prices from 2010 until now. By unwinding the conversion, the farmer may be able to then redo the conversion and save substantial tax this year.
For example, let's assume the farmer had $500,000 in his IRA on June 1, 2010 when he converted it into a ROTH. Now, let's assume the value of the ROTH is only $300,000. By unwinding the ROTH conversion, the farmer does not pay tax on the difference between the $500,000 last June and the $300,000 value now. At the highest tax bracket including applicable state income taxes, the total tax savings could approach $100,000.
Remember, this only applies if the farmer filed an extension and you have until October 15, 2011 (technically October 17 since the 15th is on a Saturday).