McCainpedia is a wiki intended to serve as the hub for opposition research for the upcoming presidential race. It's interesting because it is a example of a large and important organization using a wiki to communicate with (not to, but with) its members.
As far as the world of politics goes, it seems like a pretty novel idea to make information public like this. But I like it. I just finished reading Cory Doctorow's Little Brother, which talks a lot about how making things public actually makes them more accurate and more secure.
In the book, the topic is computer encryption. The reasoning is that if the encryption technology is made public, much smarter people than its creators will try to break it - if no one can break it, then you know it's secure. But if you keep it secret, you'll never know about its vulnerabilities until it's too late.
I like that a political party is bringing information to the public in an easy-to-use format, instead of doing all their research and strategizing in the proverbial smoke-filled, locked-door war room. It would be even better if the information wasn't just anti-McCain, but compared his positions to the democratic nominee.
I'm sure both republicans and democrats will be scrutinizing the information published here, and reporting any errors or omissions. This will lead to better information, which leads to a more informed public.
And even though the information is obviously biased, I still would consider this a trustworthy source. You always need to take the source and its slant into account when using information, but because the DNC is putting its name on this and taking responsibility for it, I would trust them to be accurate.