Yes, several. I am currently doing an animal care certificate online and studying childrens writing. It's incredibly convenient however I'm not the best at time management.
Most short courses are designed to easy to access so very basic computer skills are all you need.
Started doing my Bachelor of arts degree on-line - I loved being able to "attend" lectures at whatever time was convenient for me and submit assignments while travelling around Australia. I didn't finish my degree as I had 2 children and am now doing a totally different course - I am studying, on-line also, to be a childbirth doula. Again - I love the convenience of on-line study. Although I do find it harder to motivate myself when I don't have to attend actual classes.
Yes. But not fully. A course that I did had an online component. It was just as challenging as if I went into a actual classroom. For me, online study was hampered by many distractions from within my home.
Yes, I've taken some graphic design courses online. They really lend themselves to this media as you watch something and then replicate it immediately, being able to stop the lecture for as long as necessary to perfect a skill.
Yes. I had to do online training courses for work. I have done a post graduate course to improve my qualifications and I did two years at open university for personal development. I love to learn but don't have much time anymore.