Wikipedia is a vast database of knowledge. The double edged sword of using Wikipedia is that while most of the information is accurate, anyone can edit an article, and Wiki Trolls are commonplace. Evidently, some people have nothing better to do than to place insanely inaccurate information into the articles on Wikipedia.
Detractors will say that no one should use Wikipedia as a reference for anything, and many schools and colleges have forbidden the use of Wikipedia as a reference. College professors feel that college students should not be using encyclopedias at all, but should be researching primary sources for their information.
So is Wikipedia useless? No, it isn't, because there are many very professional and well sourced articles that can be used if you know what you're doing. Wikipedia should be used not as a source itself, but as a guide to find more primary sources to do your research.
Researchers should only use Wikipedia articles that have a bibliography. Even then, only use the parts of the article that are cited. It is the researcher's responsibility to make sure that all cited sources exist and are accurate. Not all sources are acceptable to schools, or even to certain professors or professional organizations, so it's always best to make a few checks before submitting your essay.
Keep sources within the realm of believability. For example, if you're a high school freshman, and writing a paper on viruses for biology class, you probably won't be reading the American Medical Association Journals to get information. A source that is way above your level of comprehension will stick out like a sore thumb to a competent teacher or professor.
Check your local library to see if they have the book that is listed as the source. If they don't, and your college or school library doesn't, then it probably won't be accepted as a reference. Once you find that the source book is available, check to make sure that the information really is in the book.