I recently completed 7 Udacity courses in less than 2 months. All of them are from the 'Front End Developer' nanodegree. I am not enrolled in the program, I am just taking the courses for free by watching the lecture notes and doing the short quizzes.

Pros:

1. It provides good breadth of knowledge around what is possible.

2. The style is engaging and the videos are short and well made. I have tried to take Coursera courses before, but always ended up dropping out after the first couple of lectures.

3. It gives you a specific goal; most of the nanodegree courses are geared towards completing a specific project.

4. I was able to quickly get my personal website up and running (I believe in using completely static HTML + CSS, JS when required, and the courses helped me to learn enough to quickly hack together something just using Notepad++).

5. I have plans to enroll for a Nanodegree later. It is quite affordable even for people in developing countries (like me), after accounting for exchange rate fluctuations and cost of living.

Cons:

1. The courses don't go too deep, and you won't become a master unless you are motivated enough to do the work yourself (e.g. Introduction to jQuery - it gives a flavour of what is possible to do with jQuery, but does not go into any depth if you want to be an expert).

2. What you get out of the course if entirely up to your motivation in improving yourself. Completing the courses alone won't be enough to pick up a new skill.