The stuff I've seen mostly points out that in-person is only evaluated by grades, and that grades between online and in-person are about equivalent.
Richard Mayer has done some pretty good research on learning and using computer aided instruction, however his research suggests that a great deal of traditional (in-person and online) education is not as effective as it could be...
And online learning does not occur in a vacuum. There should be an instructor who helps students to evaluate what sources are good ones and which ones are bad. In print there is good and bad too. I agree that much good material is simply not available online at the moment, but learning online does not preclude getting books or going to the library either.
People who desire to learn will learn. On-line activities are just that another tool in that enables us to venture into the global village. I disagree with N Hansen that there should be an instructor (or it maybe just a choice of words for which I apologise) but facilitates a direction into what is now becoming a society of information overload.
From my research as a Flexible Learning Leader in Australia, there is a richness in on-line that is not present within a face-to-face environment and that richness enables learning not to be time constrained. Whilst programs are generally time constrained (they need to be for assessment reasons) one can continue a discussion (like this one) outside the formal time allocation with a F2F program. The diversity also comes linking people with similar interests who are geographically separated. You must also remember that on-line can be synchronous and asynchronous, providing a richness of a learning environment outside of a book or paper based research.
IMO the richness of learning does not come for one ability to write down what one has found, but from the ability to be able to demonstrate and talk openly about their experiences and what they have learned. This removes a lot of the paraphrasing and opens the learners mind to being able to express their ideas like a story teller.
I find the internet great for online learning because I am dyslexic. I have a reader software for a browser that helps me read. I spend more time understanding and comprehending then trying to sit there for hours trying to figure out what the word is.
The other thing I love is online presentations, since I am so visual regarding pictures and such I am much able to grasp the information. I can not tell you how thankful I am for the Internet and just the IT industry . It has helped me go farther by working around my dyslexia instead of changing everything in my life.