This study that Scot McKnight quotes gives exactly the results I would expect. Lecture covers more material in a shorter amount of time, but the average learning is significantly less than problem based learning. I believe this conclusion also applies to online teaching with little lecture and a lot of discussion forums. The average student take away is greater, even though the student who best learns in "binge mode" may not learn as much.
We are now, of course, in a position to video/audio record or even have live lectures in online classes, allowing for what is sure to become more and more of a hybrid online learning experience going forward. Indeed, I know of seminaries that are experimenting with real time online classes that are just like traditional classes except the students are all over the globe.
P.S. As ideal as that may sound, in the end, most students prefer to have the freedom to get on whenever they want, which is why any electives I offer (e.g., Hebrew for Ministry that starts at the end of the month) have a one hour real time video session that you are urged to attend but is recorded so you can view it later if you cannot.