The idea that "anyone can edit" on Wikipedia needs to be severely qualified. It is intended to be an open-source version of an encyclopedia, but it does have standards, and edits that don't meet those standards very quickly get tagged or changed. Statements are expected to be sourced from books and articles, and not just from the writer's personal knowlege ("original research" is a real no-no, as are puffery, weasle words, and articles that read like an advertisement). It's a regular thing to see "citation missing" placed after unsourced statements in an article.
Often people deliberately put false information up, sometimes to push an agenda, sometimes just to get a kick out of vandalism, but these things are usually caught pretty quickly, as there is a whole herd of people over there at Wikipedia who seem to do nothing but look for problems. There are also "talk pages" on controversial articles, which is a sort of forum for people working on that article.
As for accuracy, it's about as accurate as anything else on the Net, or, for that matter, in your local library--it's a combination of good and bad information, and you have to use a little common sense to tell which is which. Evaluating claims is a basic part of reading anything, and the people on THIS board should have no problem with that, as our BS meters tend to be set with great sensitivity.
Wikipedia is a very useful tool for a quick look-up of a subject, or to find details that aren't likely to be a matter of opinion, such as names, dates, spellings, capitol cities, etc.; but the information there is not anything that you can base a solid opinion on without further research. It has a very large collection of articles, and it's unusual not to find something on whatever subject you're looking for, so it makes a good starting point for just about anything. Nearly all articles have a bibliography of sources, and links to webpages with more information on the subject.
The general opinion of Wikipedia seems to be that the most accurate articles are the ones on science and mathematics, whereas biographies and current event articles need to be approached with a great deal of caution. My own gripes about Wikipedia are that it seems to value consensus above expertise; and that they insist on a "worldwide perspective" of a subject, which leads to some bizarre things like what they call schnitzels in Brazil.
I personally use it a lot for information on movies, TV shows, and the like. I just spent a lot of time last week using it to refresh my memory about the details of one of my favorite cartoon shows,
ReBoot, and today I was zipping through pages on various monster movies while I was writing comments on the IMDb.com message boards. I tend to be very bad with names, and regularly forget the title of movies for which I can remember almost every other detail.
It puts a great deal of information at your fingertips, but with all that quantity, the quality is inconsistent.
A lot of the negative press about Wikipedia is just that, negative press. Someone writes an article about some of its problems, and exaggerate them to make a good story. This exaggerated and, in itself, inaccurate information gets picked up and parroted by people too lazy to check for themselves, and after a while it becomes "what everybody knows". As long as one uses Wikipedia with due regard to what it is and what it isn't, what its good for, and what its limitations are, there should be no problem.
