For the 2012 election, I did a lot of research on the candidates where I live, and although I generally lean left on most issues, I actually did vote Republican for HOR (he won easily, he's quite popular). I'm sure I knew more about the candidates than the vast majority of those voting.
That said, when I got to vote, and I found more things to vote for than I anticipated. Judges, mostly. I voted blue across the board on those I didn't know. And minutes after I left, I was kicking myself for doing that. I shouldn't have voted for people I knew nothing about. All I knew was democrat/republican.
My point is - I agree with Mike. I'm sure there are many, many people who just pick "their side" across the board without thinking. It's the wrong approach.