Before I went to school online, I attended 2 different colleges. I had a lot of credits and I was able to find a college (Charter Oak State College) that used all of those credits towards my bachelors. After I completed my bachelors, I enrolled in and completed my MBA through Colorado Technical University.
The key is to be very disciplined. As some of the previous posters stated, once you get behind, it is very difficult to catch up. There is a lot of written work as you have to write out your discussions, which would normally be verbal in a class setting. For me, CTU was as close to a class setting as I could get. The instructors hold live sessions each week so you can ask questions and make comments via voice or chat sessions.The instructors all have office hours if you need assistance. You also have group assignments with your classmates so you get to interact with others in the class. The only drawback was the classes were back to back at CTU so you don't get a break. At COSC, you usually get about a week to recoup before moving to the next class.
Each school is different. I would highly recommend asking a lot of questions about the format, the spacing between classes, and instructor availability. I would also ask to see a demo (if available) of the class structure.