For the most part, Wikipedia is pretty darn good. In general the articles are written by people who do know quite a bit about the subject. And they often tend to keep a close eye on the articles to make sure nothing weird gets done to them.
As a research reference, it's not considered acceptable. There's just too many opportunities for something incorrect to end up in the articles.
But for general, everyday reference, it's very thorough, contains many more articles than any encyclopedia, and is extremely accessible.