More than 100 judicial rulings have relied on Wikipedia, beginning in 2004, including 13 from circuit courts of appeal, one step below the Supreme Court. (The Supreme Court thus far has never cited Wikipedia.)
While 100 decisions out of thousands of decisions made every year may not be many citations, only a select few learned legal treatises have been cited as often as Wikipedia in a two year period. Only a couple of blogs have been cited more often (many of which appear in the sidebar). It undoubtedly outranks the law reviews of many law schools for frequency of citation. There are many actual appellate decisions that have never been cited in a published opinion (probably close to half), and the better part of the nation's statutes have never been cited to by any court.
While the linked article worries that this might corrupt the judiciary, unless a party actually introduced a Wikipedia article into the record as evidence at trial, it should only consider these matters in the course of taking "judicial notice" which is governed by Rule of Evidence 201 (Colorado and the Federal Rule numbers are the same). The basic standard is that:
A judicially noticed fact must be one not subject to reasonable dispute in that it is either (1) generally known within the territorial jurisdiction of the trial court or (2) capable of accurate and ready determination by resort to sources whose accuracy cannot reasonably be questioned.
The fact that Wikipedia is about as reliable as the Encyclopedia Britannica, is more up to date, and covers more topics makes it often desirable on this score. Judicial opinions have long referenced news articles for a like purpose. In principal, such a reference in either case, however, should be preceded by an opportunity to be heard "as to the propreity of taking judiical notice and the tenor of the matter noticed.", and request may be made on that score by a party after the fact (presumably in a motion for reconsideration).