Wikipedia is a great starting point for any topic you need to know something more about. Usually the major facts are correct and if they aren't, the article at least brought your attention to something to verify or research further which can get the ball rolling for whatever information you were looking for in the first place. It's very useful to be able to find the gist of virtually any topic on one site. Then you know what to look for in terms of real sources.
I know this is a bit off-topic, but why are encyclopedias not allowed as a source by most places? I mean, I've personally never tried using one, but I am rather curious as to the reasoning behind it. Seems stupid to me, as encyclopedias are basically big old books with facts/knowledge in them, aren't they?
If you want to use Wikipedia's sources as your sources, you need to have actually read those sources to verify they are what you want (and to have them actually be your source). You're "not allowed" to just say "OK, these are Wikipedia's sources, therefore they are my sources because I read Wikipedia.".
I believe the internet is quite possibly man's greatest invention (definitely the greatest in modern times), and Wikipedia is the greatest thing to come out of the internet.