“And Then There Were None: Surviving Foreign Language Study” Here  is my go-to article when someone brings up Rosetta Stone. It is a study reviewed in the Backseat Linguist blog.

150 government workers were offered Rosetta Stone. Only one (1) completed the training. In order to stick teaching must be comprehensible, interesting and repeated. All three elements must be involved. Too many of these on-line programs do not have all of these elements and the results are shameful. We live teachers do not do much better, so we have very little to brag about.