I am pleased to announce that I have passed my qualifying exam, which means UNC will allow me to continue on and get my PhD (assuming I actually do some research). So now that I have successfully passed my qual I will now express my thoughts on the matter.
Here at UNC-CH the department is a combined physics and astronomy department which means the astro students are mixed in with the rest of the physics students for the basic classes (E&M with Jackson, Classical Mechanics with Goldstein, and Quantum Mechanics with Sakuri, Statistical Mechanics with some book that I never heard of, nor wish to hear of again), but after that the astro students separate off into a different set of classes (Stellar Structure, Galaxies, "High Energy" (compact stellar objects, the class is called High Energy for historical reasons, and the university is being very picky at the moment and won't let the department change the name, so the professor teaching the class changed the material, room location etc. and didn't bother to tell the university. It's a little easier to do when you only have seven students in the class.)). Then when the students are done with those basic classes they then take the qualifier that consists of six written tests roughly corresponding to the classes that we have taken. In my case that meant E&M, Classical Mechanics, Quantum, Stat Mech, Stellar Structure and "High Energy".
Each test consists of five questions, of which we only have to answer three (or if we answer more, then they will only take the three highest scores into consideration). We are given two tests at a time and we have three hours to complete the two tests (for completeness, the groupings were: E&M and Classical, Quantum and Stat Mech, Stellar Structure and "High Energy"). Each question is graded out of 10 points and to pass each test a minimum of 10 points is needed out of 30 possible. If a student fails any one test then they fail the entire qualifying exam (there are some exceptions made for students who do sufficiently well on the other tests, or do exceptionally well in the corresponding class that that failure is waived). Then assuming the student passes each individual test, then the committee looks at the overall score. The overall score must be above a certain level in order for the student to pass (last year the cut off was set at 50%, I don't know yet what the cut off was for this year, but apparently I was above it). This means that a student must get an average of 15 out of 30 points on each test (assuming a cut off of 50%).
The pass/fail rate changes year to year, I have heard of years where everyone passed, whereas last year the failure rate was 20%. Anyone who fails is given another chance to pass it. If they do not succeed on the second try then they are typically awarded a masters and not allowed to get a PhD.
Now the actual tests:
Typically the professor who taught the corresponding class will submit and write at least two of the five questions for the test. The other questions come from any other professor who chooses to submit them to the qualifying committee (typically the professors who submit the questions also sit on the committee). So they try to have at least a few questions coming from the person who actually taught the class, so that if the professor emphasized a particular topic then the students will have a better chance at answering the questions submitted by that professor. But this also means that the majority of the questions came from a professor who the students never had a class from, and thus are not familiar with the type of questions they ask on exams.
Some of the test problems are actually written by the professors, while others come from various sources (i.e. the University of Chicago qual book, sometimes this can be painfully obvious as one year on a previous exam the question was copied straight out of the Chicago book word for word, including typos). Other sources include previous midterms and finals given by professors who have taught the classes in previous years. Thus in response to this, the grad students at UNC have built up a standard battery of study materials, including old qualifying exams (we have access to them, and some questions repeat on a ~5 year cycle (+/- 2 years), sounds predictable but it really isn't because it only happens on a very select set of problems, and this has only held true over the last 11 years), question and solution books for qualifying tests (including the already mentioned Chicago book and the Lim books), and of course old midterms and finals (with solutions! which we really aren't supposed to have but some how someone got a copy that has been passed around...).
So in reality for some of the subjects it doesn't turn into a test of our ability to work problems in physics, but it turns into a test of our ability to work out, memorize and regurgitate problems from the standard set of problems. Granted, for some of these subjects there is only so much that you can test on so that necessarily limits the total number of problems that can possibly be used. But some of the subject tests are actually well written and really do test our understanding of physics (or astronomy as the case may be).
For my particular studying I stuck with old qual problems, and the Chicago book, old midterms and finals, and a general review of important subjects. Specifically in the Chicago book I stuck with the stat mech portion (more explanation about that here, it was a really interesting experience). This turned out to be very advantageous because two problems on the stat mech portion of the qual came straight from the Chicago book.
Overall the tests were hard (but only two of them I felt were actually good measures of my knowledge and understanding of physics and astronomy), but from one perspective I can see why having the tests is necessary. As my adviser put it, the qualifying exam is a very imperfect method of separating PhD candidates from everyone else, but until they come up with a better method, we will have to stick to this.