if it's the only resource you're using, well then . . .  ...you can be in deep doo-doo.  I suppose, if the reason you're looking something up isn't very important, then you might be okay.  Or, even if it is important, you might get lucky and get a correct answer.  I'm sure many of the entries are; I'd even be willing to concede that most of them probably are.  
But why take a chance?  Given the facts that people make honest mistakes AND that some take perverse pleasure in...vandalism (a good word for deliberately putting misinformation  
 
  
)--give me good old, reliable sources any day:  ones by companies of long-standing reputation, known to have quality editing, etc.
*I could go in there and post oh, say, such-and-such is made by using ammonium sulfide, when the correct compound is really ammonium sulfate; then what if somebody tries this and there's an explosion or something?**  No thank you--I can't see there being very many times at all when I'd look up something in Wikipedia, because then I'd just have to try other places to check the accuracy.  Nuh-uh; nope.  
**To me, believing false facts would be the mental equivalent of having an experiment blow up--that's why I used that example.  I make a fool of myself quite well enough on my own, tyvm, without "help" that would have me running around saying, perhaps, "Christopher Columbus 
really discovered America in 1493--I read about it in Wikipedia".
EDIT:  Father Steve, thank you, thank you!  From your post in Weekly Themes (italics added):   
The entire phrase is 'the proof of the pudding is in the eating,' meaning that the true value or quality of a thing can only be judged when it is put to use.   , and  
the proof of the pudding is in the eating - proof will be in the practical experience or demonstration ...