I find Wikipedia very useful - a good first stop to finding out about some things. I'm not sure I would trust it to enlighten me about higher mathematics, but it is great for getting all the trivia about T.J. Hooker or something. Google searches for films and people, say, invariably have it as the first result, or in the first five. I am cautious, though, and aware that the content can't be taken as Gospel. At the very least, though, pages generally have links to more credible and authoritative pages, so it can be a great launch-pad to more serious research.
I have been interested to check pages about topics I myself have some knowledge of - like philosophy. I haven't always been impressed, but it's never occurred to me to presume to edit a page: I'm old school - leave it to the experts! I've also been amused by the discussion and disagreements - often conducted at a very petty level - by competing authors/critics. It doesn't always fill you with confidence in the authors. The Wiki-discussion pages on philosopher David Chalmers and on Consciousness are hilarious.