Can I quote from blogs or Facebook posts for a presentation?
Quoting from a public blog or other social network, like Facebook or Twitter, is no different than quoting from any web source. You should assess the use based on the four factors of Fair Use. Most limited quotes are appropriate as long as you include the attribution or citation.
One thing to remember, when you are writing or presenting in academic settings (like in class at JMU) the source of the information is just as important as the information itself. Many blogs post articles or other documents that were initially published elsewhere. Generally you do not cite these as contributions to a blog. Locate the original and cite that item.