Web 2.0: Info Lit

I'm getting ready to co-present a workshop for adjunct faculty on the info lit implications of the Web 2.0. My main question is: "Is user created content reliable?"

Looking back to the BPC (before personal computers) days, we classified information resources not by format but by the proximity of the creator to the information provided:

• Primary sources--journals, diaries, letters (all created by the person with first hand experience of the event described)
• Secondary sources--journal articles, newspaper articles, etc. (information gleaned from primary source)
  
• Tertiary sources--encyclopedias, textbooks, library catalogs, survey articles, reading lists, bibliographies, etc. (information gathered from both primary and secondary sources)

Couldn't Blogs and photos on Flickr be considered primary sources? When it is so easy to create content, how do we determine if the creator is indeed knowledgeable/truthful about the topic presented?