Did you find that the lectures provided enough basis to complete the problem sets? A number of students I talked to struggled to actually piece together code after the presentation of mostly concepts in lecture.
[1] http://cs50.tv
For some of the more beastly problem sets in data structures and memory management, where Googling the error message just didn't cut it, I had to watch through all that week's available content (both lectures, both recitations, the walkthrough and the shorts) before gaining enough momentum to grind by. That's where it really hurt to not have another student sitting in the next seat to bounce ideas off of. They've put together a well monitored forum but it's not the same as walking someone through your code. I got it done, but some gray hairs could have been avoided.
One of the major areas of improvement for all online ed is how to bring back that frictionless asking of questions. It's a comparative advantage for both people -- you may save me two hours of frustration with ten minutes of your time on a particular memory error and I may save you two hours of frustration in a similar fashion by better understanding pointers.