Wikipedia

Although Wikipedia is an easily accessible source of information, it is certainly unreliable. In fact, in one of my classes several years ago, a classmate edited some information on George Washington just as we were discussing the website. In just a few minutes the content had been changed (although it was fairly quickly restored) and episodes such as this prove that Wikipedia can never be a trusted source of information.
As with all things, you have to remember what the source is and who has access to it.
With a tool that is as open and free as Wikipedia is, certainly individuals and corporations are likely to edit information if it will be to their benefit and thus, as with everything, I would always make sure I got information from multiple sources. But as a resource for looking up simple facts such as September 1, 1939 for the beginning of World War II Wikipedia is a quick, if not necessarily trusted resource.