I find the wikipedia pretty reliable in most cases. A lot of good people work on it everyday to make sure it is the best source of information out there, and I respect this.
Of couse, as any other system, it has its share of errors, but the overwhelming number of members assures that most of the false information is rapidly corrected.
I don't know anything about the Teacher's Union and stuff, specially because I am not american or do I live in the US. But Wikipedia is also not accepted here in Brazil as a reliable source, what I think is demonstration of academic arrogance on the part of the teachers.
I think that people have not yey understood the capacity and the potential of the wikipedia, and it will take some time until that happens.