Robin, I think it depends very much on the quality of the Wikipedia article. I've seen some very good ones, and some very mediocre ones. I usually check out the sources used for the article, and see if they have used a variety of sources, rather than just one source, that from what can be seen that they are quality sources and use that assessment as a guide to using or not using the article. If the sources used are available online then I would always look and use them rather than the Wikipedia article.
However, the other issue I find is that while the Wikipedia article might have good sources for the biography they often don't cite anything for the birth, death, marriage dates etc, which are important details to us as genealogists.
It also irks me when the sources used in the Wikipedia article are copied and pasted into the sources section of the Wikitree biography. It creates the impression that the person writing the biography has looked at those sources, rather than just Wikipedia.