I think all the various responses seem to point to one conclusion. Different people have their own preferred learning styles. Personally, I learn best on my own and would probably be quite comfortable with online courses.
An important issue, however, which jwj has pointed out is the attitudes of employers to qualifications acquired in this manner. For vendor-related qualifications such as those offered by Microsoft and Cisco that this is probably not an issue, as employers would probably not be bothered where you got them from. However they would definitely be interested in which institution you obtained a qualification such as a university degree from.