A study by the science magazine Nature shows that Wikipedia's science entries aren't too bad when compared to those of the Encyclopedia Brittanica.
And they're a lot easier to correct.
The study found both had an equal number of what were called "serious errors," while Wikipedia had somewhat more modest errors.
Michael Twidale of the University of Chicago told the magazine that it was the Encyclopedia results, not those of Wikipedia, which should be of concern:
"Print encyclopaedias are often set up as the gold standards of information quality against which the failings of faster or cheaper resources can be compared. These findings remind us that we have an 18-carat standard, not a 24-carat one."
My own humble opinion is that Wikipedia needs advertising. Even something like Google's AdSense, placed in a box to the right of the content, and clearly marked as advertising, would likely draw enough revenue to pay for the hiring of some professional editors who could manage contributions and stand behind the process.
Combine that with Wikipedia's quick fixes (here's their current entry on the Seigenthaler controversy) and open source knowledge becomes a very good deal indeed. Only without those annoying salesmen.
One more point and I'm done with this dead horse. Would any of Wikipedia's critics publish the criticism in as detailed and factual a way as Wikipedia has? Go look at their current article on the controversy and then check what happens when the mentioned critics are called to account for their errors.
I rest my case.