what better source is there to determine whether wikipedia is a valid source than...wikipedia? thats right, wikipedia has expressed their opinion on whether their site is a valid source for information. the answer: no
http://en.wikipedia.org/wiki/Wikipedia:Researching_with_Wikipedia
First you should question the appropriateness of citing any encyclopedia as a source or reference. This is not simply a Wikipedia-specific issue, as most secondary schools and institutions of higher learning do not consider encyclopedias, in general, a proper citable source. Citation of Wikipedia in research papers has been known to result in a failing grade
http://en.wikipedia.org/wiki/Wikipedia😖chools%27_FAQ#Is_Wikipedia_accurate_and_reliable.3F
(EDIT: kmc's smilies forbid me from posting a working link, but you can use the search function)
WIkipedia, like any encyclopedia, is a great starting place for research but not always a great ending place.
(horribly understated, but none the less...)
...anyone who sites wikipedia is clearly an idiot. and for those who have confessed to using it as a direct source and are asking themselves "is he calling me an idiot?": yes. yes i am.