When edX launched its first two courses in October this year they had 100,000 people registered between them. Coursera, which alone reported over a million registrants from their April 2012 launch to the following August, are offering over 100 courses this fall. As of September, they had about 680,000 registered for those. Udacity stood at nearly 740,000 registrations to date as of August 2012, with over 100,000 ‘active’ at the start of back-to-school season. And then there are the smaller, more grassroots MOOC offerings like Current/Future State of Higher Ed, which collect a few thousand people around shared topics of interest.
That’s a lot of people, all told.
Many, of course, won't finish their courses; the attrition rate in MOOCs is notorious. There’s no filter on the front end – people register for free and thus very literally don’t have to buy in to the program of study.
But the scale of those numbers may still have effects.