The US Dept of Education announced earlier this year that we could no longer say that blended and online learning was as good as face-to-face learning. Rather, they unequivocally stated that both blended and online learning have been shown to be superior to face-to-face in post-secondary empirical studies. In a meta-study that evaluated more than 1,000 other studies, applied rigorous standards and considered only the very best, they found online delivery to be superior (full report linked to title).
The long-running annual NSSE study conducted by Indiana University last year found more collaborative and active learning among first year and senior college students enrolled in online classes. They reported "online classes seem to stimulate more intellectual challenge and educational gains." http://nsse.iub.edu/NSSE_2008_Results/docs/withhold/NSSE2008_Results_revised_11-14-2008.pdf