These wonderful, fun explanations of Web 2.0 Tools are also great models of efficient training:

RSS in Plain English: http://www.commoncraft.com/rss_plain_english
Wikis in Plain English: http://www.commoncraft.com/video-wikis-plain-english
Social Networking in Plain English: http://www.commoncraft.com/video-social-networking
Social Bookmarking in Plain English: http://www.commoncraft.com/bookmarking-plain-english