I've noticed this, too. Udacity's courses are clearly designed from the start to work well on the web, whereas many Coursera courses seem to be existing lecture

I've noticed this, too. Udacity's courses are clearly designed from the start to work well on the web, whereas many Coursera courses seem to be existing lectures broken into smaller chunks. This really sets Udacity apart, but I think it's actually the result of a much bigger advantage: Udacity isn't affiliated with a meatspace university. It might not seem like an advantage now, since they're competing with more prestigious options from Stanford and MIT, but I think the decision to detach Udacity from Stanford will prove to be a very smart choice. I think we'll see real universities take a two-faced approach to online learning: they will want the attention it draws, but will for fear of diluting the prestige value of their brands. (See the protracted wrangling over the certificates in the original AI course. And can you blame them? The brand is probably the most valuable part of a modern diploma). This is Udacity's real advantage: they don't have to worry about prerequisites, four-year graduation rates, department budgets, or the physical constraints of offline universities. They are already much more nimble and much less risk-averse than some of the other initiatives, and it will be difficult for the programs still affiliated with universities (institutions hanging on to practices invented in, like, the 13th century) to detach themselves from offline constraints and adapt to the web.