This report: http://www.ed.gov/rschstat/eval/tech/evidence-based-practices/finalreport.pdf is worth reading. The press coverage (http://www.insidehighered.com/news/2009/06/29/online) focuses on the finding that where there is a difference, online classes outdo face-to-face classes.
I've been reading the report, though, and there is a lot more in it worth paying attention to. Here are a few that stand out to me:
1. that blended courses outdo face-to-face only and online (where there is a difference)
2. that the key variable might be time, not the medium of the course--that is, that time on task is the key factor in learning (consistent with all sorts of other studies)
3. that online and blended courses excel in their ability to foster reflection and community (characteristics that are sometimes associated with face-to-face courses)
I'm also intrigued by the report's typology of online courses: expository, active, and interactive (see the table on p. 25) Seems like a smart way to think about all sorts of learning.
See the summary of findings and conclusions on pp. xvi-xvii.