Sheldon, I think you worry too much -- at least, as far as Jimbo and the Wikipedia project are concerned.
Wikipedia is a work in progress. I don't think anyone would bother to launch a libel action against it, if for no other reason than it's hard to hit a moving target.
Think about newspapers. Suppose the New York Times prints a letter to the editor from Joe Blow, saying that Merv Griffin is a cannibal. Is that actionable?
Suppose it's a signed column on the op-ed page. Joe Crow, columnist, says Griffin eats people.
Suppose it's an editorial: the NYT calls Griffin a cannibal.
Or it's a front-page article, with a headline screaming "Griffin eats human flesh!"
But then his lawyers contact the paper and say, "Dude! Whassup with that? That's grody to the max!"
The response of the newspaper to the lawyer's letter is key.
If they say, "We stand by our story" then they may have to battle it out in court.
But if they say, "Oops, you're right! We'll print a retraction" -- then what basis is their for a libel action?
Wikipedia is way different from your project: we constantly strive for neutrality on all issues; you take a definite stand on many issues. We'll never have to fight, because we're not *asserting* anything. But you're going around accusing this person and that group of deceptive PR campaigns to cover up misdoings (especially environmental wrongs), and on top of that you're planning to *assert* that you're doing so "fairly and accurately".
We march to different drummers, dude!
Ed Poor