How many people vote by party and not what the person stands for or can do in the US Presidential elections?
Honestly, I'm not aware of any studies done on this very interesting question. I think it's a good one, though.
I grew up in a Republican family. Actually, all my friends are Republican, and my entire family is Republican. The only view I was exposed to my entire life was the Republican point of view, and in the more politically active of my family's eyes, the Republican party Can Do No Wrong.
It's interesting, really. If the nation goes downhill during a Republican presidency, then my family and friends tell me that it's because of the "Democratic Congress", or that the decisions made by the "Democrat president before are coming home to roost", or that "it's not as bad as the media makes it out to be, and it's the stupidity of the people for spending money, anyway. Democrats would just make it worse."
In the past few years, I've started running into Dem's in online communities, and the superior, mocking attitude they take towards Republican's certainly explains a lot of the Republican hatred of Dem's.
For my part, I can see points and issues in both parties that I agree with. I've spoken with my friends and family a little about the candidates as I weigh the issues, but honestly, they so completely refuse to even entertain the possibility that Democrats can have good ideas that it's impossible to talk to them.
Interestingly, I know several Democrats in online communities, and they are much the same towards Republicans -- absolutely refusing to admit that there is even a shred of decency or hope for our country's improvement in the Republican candidate.
I think, to answer your question, that if a person identifies themself as a Republican or a Democrat, then they are far more likely to blindly vote along party lines without truly considering the issues and the plans the candidates lay out for dealing with them.