I took the Osler, probably the one most frequently taken by residents.
Frankly, I'm not sure how much it helped but I was able to study a great deal before the exam so nearly all of the material was review for me. I took it the week before the exam and its difficult to review all the days material after the course that night because you are exhausted and don't have enough time.
Taking it in June might be better, so you get an idea of what is asked and then have the binder to help guide your studies.
The NY General Surgery Review course is geared toward Recertification. My residency program bought me the DVD/CD course and I found it quite helpful to listen to them when I couldn't read anymore, or while in the car. Some of the lectures were better than others and more useful for the exam (ie, Esophagus was great; Transplant much too detailed). The course is only offered in November, so the timing is not geared toward the August certification exam.
Odyssey does oral exam review courses which are well done according to friends who have taken them; I do not believe they have review for the written exams.
All in all, I think I am probably an example of the typical Osler student - one who already has studied and is just using the course because they are paranoid about passing. If you can afford it, it is probably a good idea although honestly as is as par any course, some of the lecturers are sub-par and some are fantastic (the Vascular guy was great...from Mercy in Baltimore).
The trouble with the review books is that most of them that I have seen have lots of mistakes (see my reviews on Amazon). It makes it difficult to trust a book when you find conspicious errors. Others I've known have just read a textbook cover to cover...great if you can digest and remember all of that material.
There is very very little basic science on the exam, so don't cover that in detail when you do decide what, where, when and how to study.