At least for my fields of interest, encyclopediae are never considered appropriate references for college student papers—Wikipedia is not exceptional in that regard.

That said, Wikipedia is untrustworthy. It's a great way to quickly learn about ideas and vocabulary in a field, but it's riddled with misconceptions, misinterpretations, deceptive slants, and other errors. It's important to treat it with a healthy dose of skepticism and base research work on original sources instead. Regardless, though, it's an amazing resource that I'm sure has accelerated research productivity at all levels.