To answer a few of your questions:
1) The courseload is pretty intense, but I am sure you will find it that way no matter which school you attend. The information you are covering in each class isn't necessarily difficult to learn, there is just quite a bit of it so you really need to be able to prioritize your time and use good study habits.
2)As far as clinical time goes, you see your first "patients" during the first quarter of your first year...they bring in local elementary school kids and you do exams on them. We have at least one clinical class per quarter during our first year, including a periodontology class where you learn to clean teeth...you are required to do prophylaxis during your second year. You start having your own "real" patients during your third year, but prior to that, you recieve a lot of clinical practice and experience. They have us work on each other quite a bit-giving exams, cleaning teeth, etc. We also start in the lab during the first quarter doing fixed pros and waxing...these classes meet twice per week (three hours per day) and continue throughout the first year.
3)The grading system at OHSU consists of letter grades. There are occsional classes that are pass/fail, but these tend to be fairly easy classes and are usually one credit.
I have nothing but great things to say about the school so far. Everything has run really smooth and the faculty have helped make the transition to dental school relativly easy.