Cultivate an attitude of skepticism when it comes to web-based content.  If you have any doubt whatsoever about the reliability of any given website, clear it with your instructor or check with a librarian before you use it in your paper.

Here is what Wikipedia itself has to say about using Wikipedia for academic research:

• "Wikipedia can be a great tool for learning and researching information. However, as with all tertiary reference works, Wikipedia is not considered to be a reliable source as not everything in Wikipedia is accurate, comprehensive, or unbiased. Wikipedia, like other encyclopedias, is intended to provide an overview of topics and indicate sources of more extensive and academic information.
• "...you should question the appropriateness of citing any encyclopedia as a source or reference...most secondary schools and institutions of higher learning do not consider encyclopedias, in general, a proper citable source." This is especially noteworthy considering anyone can edit Wikipedia information given at any time.
• "Information in Wikipedia is often accompanied by a reference. You can use Wikipedia to find the source of the information and cite that. Indeed, Wikipedia can often be a good starting point for research to other sources of information."

When using Wikipedia for background research, it's best to follow two simple rules:

1)  Do your research properly.  Remember that any encyclopedia is a starting point for research, not an ending point.

2)  Use your judgment. Remember that all sources have to be evaluated.

For more on what Wikipedia says about Wikipedia and academic research, see:

Wikipedia: Researching with Wikipedia

You may also want to use the Cite Unseen widget, which scrolls through citations in Wikipedia articles and inserts icons denoting the type/reliability of each source listed.