When I first heard about Second Life I was very dismissive of it, but then I read several articles in New Scientist, and I finally created an "avatar" a few months ago at an IBM Conference, which helped give it an additional air of legitimacy. Since then I have been alternately enthralled and repelled: It seems to be a powerful platform for education and simulation, but it also seems infested with advertising, gambling and pornography.
Upon reflection, I realize that my feelings are roughly similar to my feelings about the Internet when the first hints of commercialization were appearing. I think this means that the whole "virtual world" thing is at a place where the Internet was circa 1992. I remember when WWW, Gopher, WAIS and other embryonic efforts were being launched. As we all know, WWW left all the others in the dust. So, the question I am pondering is: are "virtual worlds" the next big thing? I suspect that they (or something like they) are.
Free stuff is available at a variety of places including:
http://www.vtoreality.com/2007/sl-freeloaders-paradise/1384/
Many organizations offer classes in numerous topics, from newbie topics to advanced scripting/building. Hit the search button, the "events" tab, select "education" and hit "search".
Here's a great intro: http://www.ibm.com/developerworks/edu/r-dw-r-radsl.html