See also my comment here: http://www.enotes.com/history/discuss/114364
For all the reasons already mentioned, Wikipedia is considered by many to be an unrealiable source, especially if it is the major source one consults or the source of last resort. I remember consulting Wikipedia once when looking for information on Philip of Spain (husband of Mary I of England) and discovering that he was the queen of England! (The last time I checked, this error was still there.) Wikipedia is often a very good starting point when beginning research, but for a whole list of objections to it, please visit this link:
The people contributing to this thread seem to have had a lot of personal experience with Wikipedia and cite many problems with it, including many recent problems. To its credit, Wikipedia is aware of many of the problems cited here and is trying to deal with some of them. However, many critics of Wikipedia think that the most serious problems can never be solved because of the fundamental design of Wikipedia.
Wikipedia has a reputation of unreliability because it is written by volunteer contributors who are not subject to proof of qualifications. In the beginning of the lifetime of Wiki (as we fondly call it), it was quite true that one found unreliable information as often as reliable. With its ever-growing popularity and usefulness, Wiki has undergone major upgrades to the quality and incidence of reliable information available and, even now, is more often reliable than not--turning full circle from it inception. This is not to say that there is not still a long way for Wiki to go toward full reliability, but Wiki has made great strides with expert contributions written by experts in their fields. Soon--how soon, one doesn't know--but soon, Wiki will fulfill its potential of being a fully reliable online encyclopedia source (watch out, Britannica!). What a boon for all we RIGHT click/"Search Google for ..." researchers!
There is room for Wikipedia in the information world, obviously, but to rely on it as a primary source (as mentioned above) or, worse, an only source for research would be foolish. While it is probably accurate ninety percent of the time or more, readers have no way of knowing what is and isn't accurate information. What I have come to appreciate and use most on the Wikipedia site is the bibliography. It's a good place to begin tracking down original (primary) sources and also an excellent resource for related search topic ideas. I do not allow it to be used as a research tool in my classroom, but I realize it can serve a purpose in the research process.
Most of us have learned from instruction on how to do research papers that going to secondary sources does not always provide reliable information. This is the problem with Wikipedia; it is not a primary source.
There are lots of positives about Wikipedia, and I am sure that I am not alone in using it myself to find out about a lot of topics and using it as an initial reference point. However, the way that it is open source and entries are created by users and edited by users means that we can not always vouch for the accuracy of entries in the same way that we could in an old-fashioned Encyclopedia. Often, as #4 points out, there have been cases of mistakes. They are normally corrected quickly, but this suggests that we should never use Wikipedia as the final source of information on a topic. It is a usual lilypad which we can use to jump to other sources of information, but I always tell my students that they should always use another source as well.
Wikipedia is a very large database, with some useful information within it. It is very user friendly, and easy to navigate, with a huge volume of entries. The fact that these entries are user-generated is the problem. For example recently, a high profile politician goofed up on some historical facts during a public appearance, and her supporters quickly edited the Wikipedia entry for Paul Revere's Ride to sound as though there was no goof. It was quickly corrected, but in lower profile entries, such as most of them are, it is difficult to check them all for accuracy before they are posted.
It's a good idea to be cautious of anything you read on the web, even here. The internet is a quick and easy to use resource, but it's not infallible.
Pohnpei is right on target with his answer. Unlike, for example, the Encyclopedia Brittanica or The New York Times newspaper service, precise editing and adherence to strictly factual material are not among Wikipedia's strong points. Wikipedia remains a useful and quick-to-access source for many subjects--actually, virtually any subject--which explains its popularity in today's Internet-dominated world. I use it daily, but I also find factual mistakes occasionally. Wikipedia tends to allow more subjective, opinionated information to be posted and, as previously mentioned, that information can also be edited by virtually anyone--by sincere individuals and/or by people who deliberately include false or misleading information. So, users must always take what they read on Wikipedia with a grain of salt.
Wikipedia is not always an unreliable source. However, at times, it can have false or mistaken information. This is generally more true on esoteric subjects.
Wikipedia can be susceptible to having errors because literally anyone can edit an article on the site. This means that people can put in false or mistaken information and there are no editors to fact check the statements. Other users may fix errors that they find, but little-known subjects with few experts may not get fixed because there are few people who know much about the subject.
Wikipedia is also prone to short-term mistakes such as the ones shown in the article in the link below. These mistakes are generally corrected quickly, but people who look at Wikipedia while the errors are still up can be misled.
It is an unreliable source since anyone can change the information on it.
Wikipedia is an unreliable source because regular, everyday people are the people who are writing the articles. Therefore, some of the information the put up may come out as wrong, unreal, and / or biased. This is the reason why Wikipedia is an unreliable source.
Wikipedia can be unreliable because almost anyone can go in and modify information. It is hard to tell if what is there is the truth or something that has been modified by someone that is not creditable. Although Wikipedia can seem useful double check your information with a reliable source.
Despite the 'benefits' you see fit with Wikipedia, such as how fast and easy you can acquire the information, how concise the information is, and how you don't need to read that much in order for you to to get the information you want, it is unreliable because anyone can put whatever information they want and this results in getting the wrong information.