I wouldn't trust it 100%, but i do think that it is an excellent starting point. Aside from anything else, it may help you to find other references.
In addition it is moderated, and answers checked for authenticity. This was after former journalist John Seigenthaler sued, after false information was put on the site.
http://news.com.com/Is+Wikipedia+safe+from+libel+liability/2100-1025_3-5984880.html
I know also that it is checked, as my boyfriend decided to see if he could be funny and put some stupid answers in.
It initally went up, but was soon removed, and the nest time I logged in using that computer there was a message saying there was a 'playspace' for that sort of thing.
So there is some measure of control, but opinion may be disguised as fact.