From my experience on Wikipedia, unsourced articles are very unreliable and may have plenty of wrong facts. Most of thse wrong facts are not added due to malice (though that is not uncommon), but they were added by people either from their (inevitable unreliable) memories, from blogs and forums, which, on average have an awful lack of accuracy or they are simply misinterpretations.
From my experience with Wikipedia, unsourced articles are generally very accurate and moderately precise. When I find them in areas for which I'm familiar with the body of knowledge and reliable sources, I will spend time to go find the appropriate citations and sources as time allows, to "back up" the already existing content with appropriate references.
"Accurate" and "reliable" are not synonymous. Just because the article happens to have everything right does not make it reliable, because there is no way for you to know that it has everything right.