The US Department of Education have recently published a report which analysed the findings of over 1000 empirical studies of online learning published between 1996 and July 2008. The report has concluded that
In recent experimental and quasi-experimental studies contrasting blends of online and face-to-face instruction with conventional face-to-face classes, blended instruction has been more effective, providing a rationale for the effort required to design and implement blended approaches. When used by itself, online learning appears to be as effective as conventional classroom instruction, but not more so.
Or as Joe Wilson tweeted: