When it is worth to get online MBA

The number of online MBA programs has exploded recently. Many established schools (but also new ones) offer online or distance MBA education. All programs differ considerably in the quality, length and prestige.
Of course online or part-time MBA courses are considered to be less prestigious than well established full-time MBA courses. Chicago MBA will be by far more prestigious than any part-time MBA course, unless its part-time MBA of... the Chicago GSB. Yes, Chicago GSB has its part-time MBA program! And it's not written on your degree that it was earned part-time. It is absolutely the same degree as standard Chicago GSB degree.
And what about other, less popular part-time or online MBA degrees? Is it really worth to pay bucks for any less popular online program?
The answer is as always: it depends.
If you are not working full-time, or you want to make a break in your work full-time is probably the best investment for you if you think about the managerial position in the future. Full-time MBA is also a good place if you want to build your network (but don't over-estimate networking - networking is not a most important element of the MBA program), have a wonderful time in your life or if you just want to look for the new job (during the full-time MBA program looking for a job is one of the most important activities).
However, if you already have a good job, you have family or you don't need "holidays" from work you should consider on-line MBA from the good school. This is especially true if you already have reputable education on different level (let say good MSc or CFA), but you need an MBA to be eligible for managerial position. If this is not a top-ten MBA program no one will look at the name of the university anyway, neither on wether this was full-time or part-time program. The most important will be that you have an MBA.
Of course you may find different online programs. You should analyze how much you want to learn and how much you want to pay for it.
Also the quality of different programs is various. Just compare some programs like: Instituto de Empresa MBA, Regis University Online MBA, Robert Kennedy College in Swiss, Frederick Taylor University and you will see that quality and level of fees varies hugely.

To conclude, I would say that not always is an online MBA degree useless. Sometimes, especially when you have good prior qualifications, online MBA may be the smartest route that would lead you to the managerial position in the company you are working in. And maybe even if you could combine online MBA program with learning to other qualification (for example CFA) simultaneously that would make your position on the job market similar to that if you finished very good full-time MBA program