Since 2005, the Educause Learning Initiative has been releasing a series of briefs–one a month–outlining new and emerging learning technologies. Each brief starts with a plausible scenario that introduces the technology in question. The brief then asks the following seven questions:
* What is it?
* Who’s doing it?
* How does it work?
* Why is it significant?
* What are the downsides?
* Where is it going?
* What are the implications for teaching and learning?
The answers to these questions varies depending on the technology.
Here is the answer to the last question excerpted from their brief on Wikipedia (June 2007):

What are the implications for teaching and learning?
Wikipedia blurs the line between consumption and creation of knowledge, giving motivated students the opportunity not only to use but also to generate knowledge and see themselves as members of a community of learners. Wikipedia offers students an opportunity to hone their research skills—by evaluating its content against other information sources—and to engage in a global community of collaborative content development. Students can
see how knowledge is created, participate in that process, and understand when their comprehension of a topic is sufficient to make a valuable contribution. Some learning theorists contend that content creation and analysis is a necessary component of learning. Wikipedia can encourage students to analyze what they read, ask questions, and engage in reflective, creative learning.

Wikipedia is a highly controversial topic, especially in the academic world, since it is very difficult for people to evaluate the veracity of the information. I’ve heard that in many instances Wikipedia actually rivals Encyclopedia Britannica. However, on particularly controversial topics–especially those that involve politics, pop culture, or current events–Wikipedia can be worse than useless.
In my own experience, I often use Wikipedia as a starting point when I go looking for information. It can be a very useful aggregate of related information that can then lead me down many different paths until I find information that I can feel confident is fairly accurate and reliable.
In any case, if you are interested in learning more about the Educause Learning Initiative’s "7 Things You Should Know About…" series, then visit their web page for the latest information. The EdTech home page also has links to selected briefs from their series.