The first thing I thought when I saw McCain had picked a female was Oh Crap.
I know this is based on limited exposure to Hillary supporters and will probably sound misogynist but I'm talking about gut reaction here so...
I've met several Hillary supporters and the only reason they gave for supporting her was because she was a woman. They all thought it was time for a female president. Never any talk of her policies or political practices. So with this pick, I really believe that the number of Hillary supporters voting for McCain will most likely rise significantly. It doesn't matter who she is, what her policies are, what scandals she has been involved in, etc. The same people that supported Hillary just because she was a woman will flock to McCain now.
I'm saying this because the only Hillary supporter I have ever met supported her only because she was a woman (I don't want to ever meet hufflarry2000).

Oh Crap. Eight is enough but there may be four more...
We've got some work to do.