The answer depends on your tax rate now and expected tax rate when you plan to take withdrawals. Also, you should consider this only if you can cover the taxes with funds from outside of your IRAs, otherwise you are forfeiting the tax deferral on those funds.
For example, someone with a low tax rate now, from large losses, large deductions or low income, may have less in taxes to pay now so that the rate of tax is less than what it could be in the future, making converting a wise financial move.
As a separate matter, the taxes can be paid over two years, however, if you expect a higher rate for 2011, the interest you earn will not make it worth waiting.
Someone with high taxes now, or in the AMT, would be a bad candidate for converting.
If you are considering this and want more analysis, we created a tool for that purpose so let us know.