McCain probably didn't want to tie himself to closely to the Bush administration, and IIRC she wasn't all that enthusiastic about being VP anyway. Plus, McCain wouldn't have been able to lock up the racist vote.

I think Americans have a favorable enough opinion of Condoleeza Rice that she'll have a future in politics in the US. She's the most powerful black woman in the US (with the exception of Oprah ) which is no small accomplishment.