* Udacity really tries to learn how to exploit the on-line medium well. Coursera tosses courses not that different from a capture of the normal university course on-line. Coursera instructors have minimal support in how to put together a good on-line course. This comes across in a huge number of ways (as with Khan, you're being tutored, not lectured at, with tight integration of questions/videos, etc.).
* Udacity courses have massive post-production. There's a big difference between a professional recording followed by editing, and a professor with a webcam and a tablet on which to capture PPT slides.
* Udacity courses target a narrower range of subjects, and so have appropriate technologies to teach those subjects. Coursera is one-size-fits-all. It really doesn't work well in many contexts.
The major downside of Udacity is related -- they mostly target intro CS classes. Coursera has a much broader selection of richer classes.
It's a little like the Apple approach versus the Microsoft approach. Udacity has so many amazing details like the camera fixed above the teacher's hand as s/he draws.
Coursera's algorithm course felt like every mediocre YouTube video. It has little to do with Salman Khan's idea of an online university. They seem to employ a quantitative approach compared to Udacity. You also hear a lot of announcements from Udacity about courses that didn't make the cut, because it fell below their own high standards.
At one point, Coursera will have to remove some of their courses from their website, because they are so poor, and it's going to be a mess. I like that Udacity are already very careful about what they put up. That way, they don't waste people's precious time either.
* Udacity really tries to learn how to exploit the on-line medium well. Coursera tosses courses not that different from a capture of the normal university course on-line. Coursera instructors have minimal support in how to put together a good on-line course. This comes across in a huge number of ways (as with Khan, you're being tutored, not lectured at, with tight integration of questions/videos, etc.).
* Udacity courses have massive post-production. There's a big difference between a professional recording followed by editing, and a professor with a webcam and a tablet on which to capture PPT slides.
* Udacity courses target a narrower range of subjects, and so have appropriate technologies to teach those subjects. Coursera is one-size-fits-all. It really doesn't work well in many contexts.
The major downside of Udacity is related -- they mostly target intro CS classes. Coursera has a much broader selection of richer classes.