When we opened our shop we were adimittly against online scuba training for all the reasons that have been posted in this thread.
We are now an SDI shop and really took time making this decission b/c as an SDI shop we have to offer the SDI Online course. Both may partner and I took all the Online courses they offer and were very impressed!
1) It presents the information in all 3 ways learning is achieved; reading text, auditory and visually.
2) It is separated in to sections and are not allowed to move to the next section until you have scored a 100% on the section review. It does not repeat the same questions if you have to take it more than once.
3) It would be hard to fail the final because you have to have a good understanding of the information just to get to the final exam.
As far as the 1 on 1 time with the instructor, SDI requires a 3 hour course review before the pool with the instructor. The you have the pool time.
Our conclution was that the Online course was superior to the classroom, the main reason is the SDI knows that all online students get the information that is presented to them. You do not have the same confidence in instructors in front of a class. I know that the instructors a required to present the information! I am not trying to say they don't, nor am I trashing anyone, I am just saying that sometimes information does get skipped over b/c instructors are human.