If 70 1/2 and required to withdraw funds from my 401k rollover IRA, what is the penalty for not complying until 71 1/2?

As I understand it, the percentage of withdrawal at 70 1/2 is based on the balance in the account at the end of the year before, which in my case would be Dec 31, 2007.
As there was considerably more in the account at the end of last year than there is now, I am considering putting off the withdrawal until the market stabilizes which could be another six months or even a year.
I also know that the extension for withdrawal is April of the year following becoming 70 1/2. If the markets remains in such a state of flux, what will be the penalties I am likely to incur by not withdrawing in a timely fashion?