Wikipedia is a double-edged sword that has sharp pointy bits of death embedded into the grip of the hilt. Even if you manage not to cut yourself on the edge, you run risk of damaging yourself with it even if you're careful.
What is Wikipedia?
Wikipedia is a crowd-sourced information bank. It is an encyclopedia that anyone, regardless of qualifications, can modify if they create an account. What exactly does this mean, you ask? I'll break it down a bit for you.
wiki (plural wikis)
Wikipedia combines the power of an encyclopedia with the flexibility and modern technology of a wiki.
How should Wikipedia be used?
Very carefully. Because Wikipedia can be changed by anyone, the information may be inaccurate. It is safer to assume it isn't correct than to gamble that it is. However, Wikipedia can help writers get a ‘basic idea' of a concept for researching. For example, let's assume you want to write a steampunk novel.
By searching Wikipedia for the Victorian era, you can learn the basics of the era and have enough of an idea to know what to search for in google. This is extremely valuable, as targeted searching is how a good researcher learns about new things. Wikipedia best serves as a stepping stone, not as your ‘final answer'.
Can Wikipedia be accurate?
Absolutely. That said, because it can be changed by anyone at anytime, you need to be cautious. Inaccurate information and myths have been spread by changing entries in Wikipedia in the past, and it'll happen again in the future. Always support your information with reliable sources.
However useful and awesome Wikipedia may be, it is not a reliable resource.
Good luck with your researching endeavors!