PPP runs the numbers:
Only 28% of voters in the country think that Palin is capable of defeating Barack Obama while 60% think she is not and 12% aren't sure.
More importantly:
[L]ess than half of Republicans think she's capable of beating Obama- 48% think she would be able to, 37% think she would not be able to, and 15% have no opinion.
This of course does not mean they won't still vote for her.