This week's Library Blog entry cites an article where several authorities discuss problem entries in Wikipedia, the online encyclopedia that anyone can edit.
As a counterpoint, I'd like to offer Errors in the Encyclopædia Britannica that have been corrected in Wikipedia. I suspect if we undertook an exhaustive search, we'd learn that there isn't an encyclopedia on the planet that doesn't have issues of quality and authority.
Authority is the primary issue you will have using Wikipedia as a reference source. Since anyone can edit, you stand a good chance of coming across an entry containing errors. But even reference sources that are reviewed – like Encyclopædia Britannica – can have some errors, and information changes over time. The Wikipedia article on errors in Britannica doesn't back away from Wikipedia's own shortcomings. In the introduction to the list of errors in Britannica, the authors state:
It must be noted that errors are but one measure of the quality of a reference work. The level of trust one has in a reference work is built from the uniformity of high quality entries, the repeatability with which accurate entries may be found at random, and the lack of entries that are either wholly inaccurate, or heavily biased, among many other measures. Wikipedia is a work in progress in this regard.
Wikipedia is by its own admission a work in progress in many regards. Caveat emptor. Don't go with just one source. But don't dismiss this source out of hand, either. Approach your research with a critical mind, not only to your subject but also to your sources…all of them.
Question authority.