I did the bulk of my master’s degree (library/information science) online and overall I enjoyed it. As you note, you don’t have to commute to campus, nor do you have to attend at any particular time (usually; sometimes my online classes had set meeting times like regular classes). I worked full-time throughout most of the degree, and being able to make my own schedule was often the only way I survived. Plus, attending class in jammies with beer in hand is priceless.
What I found the hardest was getting to know people. That’s something I’m bad at anyway, and in online classes it’s nearly impossible because there aren’t any opportunities for casual conversation (when I graduated in May, I didn’t know anyone’s face except the department office staff!) My professors often assigned group projects to help overcome this barrier, but doing a group project via chat is stupid at best. However, if you just want the degree over with, then this part doesn’t matter so much.
Also difficult, and also as you noted, was putting any real effort into the classes. I would put off the reading until tomorrow, and tomorrow, because I could, and then a whole week had gone by and I was behind. I’m a terrible procrastinator, and learning online only exacerbated this for me. I found keeping a day planner with all of the work I had to do in it helped a lot in this regard, because I could see everything I wasn’t doing.
The other thing is that online courses tend to be more work than regular ones. In addition to reading the lectures, preparing questions on the lectures, doing the assigned reading, and doing the assignments, my professors all expected that I would check in and post to the discussion boards daily or every other day, which takes more time and effort than just attending a regular class. The assignments also tended to be more difficult and time-intensive than regular classes.
One advantage to online is that you get a lot of practice composing emails and postings, which these days is a real job skill that surprisingly few people have.
In short, I wouldn’t do it just because it’s there. I would only do it if online offers a real advantage for you over traditional. My school recommends that students new to online courses take only one their first semester and do the rest traditional, just to get the feel of it, and after that, do whatever mix of online/traditional seems appropriate to you. From what I’ve seen, that’s a pretty good way to do it.