Bob,
It makes more sense to use other assets (assets in non-IRA accounts) to pay the taxes for the conversion. Also, if tax rates are increased before then, the benefit of making the change will be reduced. I think lots of people will think about doing this but relatively few will actually do it. So I don't think it will have much market impact.
The real monster that could affect future stock values is higher tax rates. That's why I'm not a fan of Senator Obama's tax plans.
Scott