It's the policy of the wiki to embrace free speech where-ever possible. Does anyone have any experience fighting this kind of stuff? I don't even know a lawyer that could advise me on what my rights are as a host and/or how much it would cost to contest it.

Slashdotters seem to think the letter isn't legit (http://tinyurl.com/fakedmca), but obviously slashdot comments won't sway a judge.