A NJ Appellate Division court says that Wikipedia is too malleable to be used as evidence in Palisades Collection v. Graubard, A-1338-07.
"[I]t is entirely possible for a party in litigation to alter a Wikipedia article, print the article and thereafter offer it in support of any given position," an appeals court held. "Such a malleable source of information is inherently unreliable and clearly not one 'whose accuracy cannot reasonably be questioned,'" such as would support judicial notice under New Jersey Evidence Rule 201(b)(3).
The decision reversed an opinion by the lower court that the Wikipedia entry could be admitted under the provision that describes the type of material appropriate for judicial notice.
The issue of vandalism, or deliberately altering Wikipedia content and then printing it to tender as evidence, was raised by the court.
The reliability of Wikipedia is discussed by an entry on Wikipedia itself; its accuracy can approach that of mainstream encyclopedias.
Perhaps if Wikipedia entries were entered as evidence along with talk pages and all major revisions it might be treated differently.
But at that point it's probably easier for counsel to just photocopy a page from Encyclopedia Britannica.