For me a good score is between 70 - 80 and a miracle is >80. Whereas for the VN'ers >90 is good and getting 100 means you have achieved your goal. I seriously am at awe with you guys.
Having said that, this is a very subjective question.
This year, subjects like vector calculus and quantum mechanics & special relativity where I got 76 and 78 respectively. I personally didn't think these scores were that good since they didn't reflect the effort I put in.
Subjects that I find really difficult I'm usually happy with >60. Even though getting scores >60 don't really aid in me getting that 75 average I DESPERATELY want, so I usually get upset with my results.
THE worst score you could get is <50.
As someone said P's get get degrees. I want to add that by getting >70 secures masters and gives you confidence to feel that you are competent enough to do postgraduate studies.