I have taken a few online classes towards my master's degree. The particular program that I'm doing (at
University of the Sciences in Philadelphia), which is part-time and is geared towards working professionals, offers some online classes, some on-campus classes, and some classes that are both (some weeks you meet on campus and some weeks you meet online). I find that it is challenging to try to work through the material yourself, because although professors post "lectures" online, it is
quite different than witnessing the lecture and being able to interact with the professor and stop him/her when you don't understand a concept. I also found it somewhat difficult to motivate myself, since I didn't feel as accountable for my work as I did when I actually had to present it in person. However, online classes are very convenient, especially when the alternative is sitting in rush-hour traffic in order to get to campus for your class. And, as long as you are getting a degree from an accredited university, I don't think it matters whether you attend online or if you attend in person.