Do we trust in Wikipedia?

Wikipedia as we know is a important source of information, which is different of all of the others, because everybody can add information in an individually way.
But is it good?  as we can see at the university, most of the times is not a valid source of information, so we don´t trust in what is written there..
It is good that is a common knowledge which is share around the world, but when you don´t know exactly the source is not very trustable.
Sometimes we could read there events that still didn´t happen as some murders in USA, where the killer writes before do nothing what he wanna do.
So here is the problem, in the place where everybody can write and give information, and different points of view, sometimes are not well used, and when are well used as we don´t know exactly the source we don´t trust neither, however i am sure that it is used much more times than it is said.
The projects of common knowledge in my opinion should be always trustable, and it happens when you know exactly the sources.