You can still decide as late as October 15th (if you extend filing of your tax returns) to either recharacterize or pay the taxes in 2011 and 2012 instead of on your 2010 taxes for your 2010 conversion to a Roth IRA.
Recharacterize – if you have the misfortune of losing value on the IRA after converting, you can “un-convert” by “recharacterizing” the Roth IRA as a traditional IRA using an IRA-to-IRA transfer (do not distribute funds to yourself, as that distribution voids the recharacterization). You can do this for all or a portion of the account. Once you do so, you cannot convert again until later of 30 days after the recharacterization or the year after the year of the original conversion.
This strategy is useful to address a decreased IRA value or to shift the conversion into future years with less income, so you are in a lower tax bracket.
Tax payments – 2010 is the only year where you can choose to have the income of the conversion split in half and carried onto your 2011 and 2012 tax returns. This (1) spreads the time to come up with funds to pay the taxes (you never want to use the funds in the IRA as that defeats the purpose) and (2) gives you earnings on funds already available to pay the taxes until the payment due date.
Note: if you are paying taxes on the conversion with your 2010 taxes, the amounts are due April 18, 2011, even if you extend to have the option of recharacterizing. If you do recharacterize, then you will have over paid and have a refund due …. until you convert again.