Due to the lack of face-to-face interaction online (unless you have the ability to capture lessons and/or Skype, of course), students will read into the design of the typeface that you use. Interested in alienanting them all in one fell swoop? Use something visually heavy and angular such as "Impact." Want to be mistaken for passive and childish? Aim for "Kristen ITC" or any other font that looks like a child's handwriting. Trying to come across as a professional? Use traditional fonts -- "Times New Roman" and "Courier" are good choices. Finally, if you want to make it look as if everything you say is a suggestion and of little consequence, use "Comic Sans." If you don't believe me, consider the fact that companies spend billions on advertising each year to get our attention and our money. Or, if you're interested, I can point you to the disseration that sucked three years out of my life... ;)