According to
this one, a sizable portion of Clintonistas plan to vote for McCain, but it dates from March, when Hillary was still claiming to have a chance of winning.
According to
this one, there may still be some disappointed Clintonistas who are threatening to vote for McCain, but no numbers are given, and the threat, if that's the proper term, comes off as pretty empty.
This part seems to sum up their feelings:
"I'm not sure if I would vote for him, but I would not vote for McCain," Ms. Ramirez, a finance student at Baruch College, said. "I guess it will come down to the lesser of two evils."
According to
this one, McCain hasn't won the votes of female Clintonistas.
It looks to me like the hype about Clinton supporters voting for McCain in any significant numbers is just that: Hype.
But I could be wrong. Let's not discount the voters who want someone who looks more like themselves in the white house, regardless of the issues.
There are some significant issues separating Obama and McCain, but I'm not so sure that the same could ever have been said about Obama and Clinton. The difference seems to boil down to electing the first woman vs electing the first black, both of which are peripheral issues at best, IMO.