Personally, I think the passing rates should be pretty high (in the 80%-90%+ range) for first-time test takers. If the program that you graduated from doesn't think that you'll do well on the exam within the first 2 attempts, then they probably shouldn't let you graduate from that program. Plus, their passing rate is a reflection on their program, so they WANT a high passing rate!
That's just my opinion though; that was definitely a factor for me when deciding where to apply to and where I eventually accepted to go. It gave me an indication of how well prepared students from different programs were for the exam.