I taught a class to students on how best to use Wikipedia. It had a power point slide show and everything. It was a lot of fun.
The upshot was...never, never, never use wikipedia as a primary source. If you use wikipedia as a source, and CITE it, you will fail the assignment in any class of mine, and you probably won't get a decent grade in any other class, either.
However, Wikipedia is a great first place to go when you start collecting data. Most wiki articles provide sources. Go there. Cite them.
It's also a great place to go if you can't find information about your topic anywhere ELSE. Again, wiki will probably have an article on it, and that article will probably provide sources. Great time saver, wikipedia.
Just don't ever, ever, cite it or use it as a primary source.
Ever.
Unless, of course, you are on a religious debate forum and you think you can get away with it.