I think how you study has a lot to do with what you want to accomplish in school. If P=MD is ok for you, then I definitely would say skip all your classes and study on your own. If you are a gunner, however, and are really trying to ace all your classes, you might find that you just miss too much key info by skipping class. You really have to be willing to kill yourself if you want the H, and make it your top priority, because chances are at least 15% of your class are thinking the same thing.
It depends a lot on the individual professors: there are some who write outstanding lecture notes that have all the information you need or will be tested on. In that case, by all means skip the class. However, I've found that at least at my school, some of the profs are vindictive bastards who take it as a personal insult if students don't attend their class, and therefore either A) write incomprehensible notes, B) cite 3 chapters in the text for every lecture, or C) write ok notes, but toss in bits here and there on the side during class and then test you on those bits.
In these cases, you pretty much have to play their game and go to class. I always tried to write down everything they said that wasn't written in the notes. After an exam or two, when you've seen some of their questions, you can almost develope a sixth sense about when a prof is mentioning some obscure fact and inwardly gloating over how many students aren't paying attention and will get it wrong.
The key is knowing the profs and their style of questions. MD's tend to be more laid back, and often will tell you what two facts you have to know from their lecture for the test, so going to class for these can add up to easy points. Another thing - if you're super motivated, read the lecture notes before class and try to understand them - then you won't be wasting your time in class and will actually be solidifying knowledge in your head (although I admit, I was never motivated enough to do this - but there are always a few people in each class who do!).
Another tip - the more ways you approach the material, the more connections you will form in your brain, and the more you will be able to recall. Especially if your learning is active rather than passive - you can read and highlite the material eighteen times and when someone asks you a question, you find that you can't recall any of it.
My own strategy: I tried to go to every lecture I could, or listen to the tape if I missed so I could hear the material at least once, then I basically went over the info and wrote everything down in a notebook. Everyone thought I was crazy because I obsessed about getting absolutely every detail down, but it's those obscure details that are the 10-20% of the questions designed to separate the P's from the H's, and even if I couldn't recall the answer directly, having written it down and understood it at least once before helped guide me (sometimes subconciously it seemed) to the right choice.
Ok I know I'm a freak.
Hope any of this helped.
...there's no high pass in there?!!
