Intuition pretty much nailed this one for me.
I have spent years in contemplative training; different methods of meditation, awareness training, breath training, working with others who have wildly different backgrounds, ideas and experiences...
For me, this has led me to develop my 'own' version of open-mindedness, which i consider to be the ability to be present with another person or group of people, without re-acting to them or their thoughts.
It does not mean I need agree with a single word of anything they have said, but it means I don't have a visceral reaction in my own body that closes the ability to communicate with them, both verbally and physically.(Remember as much as 90% of communication is non-verbal)
For example:
I was in MX recently and was watching a local performance. A drunk man approached me and started railing about Bush, and then proceeded to talk about God. I had no reaction to him one way or another. I simply remained open to his ramblings and treated him with compassion. Whether i agree or not is irrelevant. The ability to remain emotionally neutral, mentally available, and physically present is my definition of open-mindedness.
I can certainly foresee things that would more than push my ability to remain in this state of mind, but i find hit highly doubtful that i will ever actually encounter such things in my life, as they are not people, situations, or events that i would seek out in any way.
I really think open-mindedness is about not reacting to other's views or thoughts, and maintaining the ability to be present, not checked out, simply because you dont 'believe' or understand what they are talking about and/or why.