I must plead guilty - I myself have added to Wikipedia's store of information (or squirrelly pack'o'lies) - mostly adding additional sections of information to existing pages. I've noticed that some of the information in the pages I worked on was a bit 'off' - not necessarily wrong, mind you, but not stated in a way that I thought quite standard for the field (this was on pages dealing with subjects I'd taught in college). I made changes where I thought they were needed, and occasionally asked for clarifications in the page discussions - generally these went unanswered, and I went ahead and made the changes when I had the ambition.
Based on these experiences and others, I think anyone expecting Wikipedia to be or become 'authoritative' in the same way as, say, the Encyclopedia Britannica, is going to be forever disappointed. It's a great first stop, a place to go when you just want to know "Who was Heinie Manush?" or "What the hell is a Cohen-Macaulay ring?" or "How high is Mt. Elbert?" Sort of like an incredibly-knowledgeable neighbor - "Hey, Bob, you know anything 'bout the John Day River?" But I wouldn't trust anything on Wikipedia that I couldn't independently verify. It's a great information aggregator - but a middling information guarantor.
In addition to the problem of incomplete or incorrect information is the problem of malice - if any reader can be a writer, any reader can be a vandal as well. The loss of complete editorial control inherent in a open wiki can be pretty unnerving to the operator, as well as reader/writers; in earlier, more innocent times I often heard wiki advocates assure doubters that with a little persistent correction, vandals and cranks would just give up and go away. Alas, even the most dedicated of editors is no match for a relentless onslaught of cranks and wikispam robots, and eventually wikis and wiki software had to put much more time and energy into preserving their data.
A look behind the scenes at Wikipedia reveals some of what must go on every day to keep entropy at bay; the administrative page devoted to 'Vandalism in progress' is extensive (though, it must be said, not so bad considering how many pages there are in Wikipedia total). Struggles against the repeated attacks of dedicated cranks and trolls are described therein; my current favorite (sure to linkrot away soon) is "Wikipedia is currently the target of vandalism by the followers of a self-styled god named Sollog..." Even with the question of accuracy out of the picture, Wikipedia requires a group of dedicated volunteers just to keep itself from decaying into a mass of outlandish crap.