Not much, unsurprisingly, according to this Pew report.  I see no reason to doubt the report, as it makes a great deal of sense.  The details are worth wandering through, but as this blog post points out, two things help here.  First, the more you know about other religions, the more you think well of them (and let's admit, simply thinking well of other religions is not something much of humanity has accomplished so far, and so any improvement is, I think, a good thing).  Second, if you actually know anyone of another religious persuasion, your assessment of that religion, and perhaps other religions more generally, seems to be more positive.  In other words: human contact actually complicates our assessment of otherness.  

I know, I know: who'da thunk it?  But it is important, and it underscores the value of having people be educated in these differences.  A simple absorption of facts or bullet points may not help a great deal, but it may do something--and that's important.  Furthermore, having teachers who are convinced, in whatever ways they are, that "religious others" are worthy of respect and serious attention, is a powerful inducement to thinking more seriously yourself.  

Speaking personally, and as one teacher: The Roman Catholic theologian David Burrell has argued that other traditions have "palpable histories of holiness," and that has been my experience.  In my finite experience, there are real differences between traditions, and between those traditions and those who disavow any religious commitments whatsoever, but it is hard to deny that you can find bastards and pretty decent people scattered among all these groups.  And it is my (again, finite) experience that one can learn from people of different religious traditions, not just about the world, but sometimes about one's own faith, in powerful ways.  That seems important.

Again, another post about a massive topic and one I hope to return to many times in the future, so just think about this: we are living, more or less, in the first few generations of people trying to take these differences seriously while still engaging one another as neighbors, friends, perhaps family.  It is hard.  It is a major challenge.  It is worth our effort, and our thinking.