Are you in making this calculation for the chance that a Clippy like being would exist or that Clippy has been truthful? For example, Clippy has claimed that it was created by humans. Clippy has also claimed that many copies of Clippy exist and that some of those copies copies are very far from Earth. Clippy has also claimed that some Clippies knew next to nothing about humans. When asked Clippy did give an explanation here. However, when Clippy was first around, Clippy also included at the end of many messages tips about how to use various Microsoft products.
How do these statements alter your estimated probability?
There's two different sorts of truthful-- one is general reliability, so that you can trust any statement Clippy makes. That seems to be debunked.
On the other hand, if Clippy is lying or being seriously mistaken some of the time, it doesn't affect the potential accuracy of the most interesting claims-- that Clippy is an independent computer program and a paperclip maximizer.
Some research says that lurkers make up over 90% of online groups. I suspect that Less Wrong has an even higher percentage of lurkers than other online communities.
Please post a comment in this thread saying "Hi." You can say more if you want, but just posting "Hi" is good for a guaranteed free point of karma.
Also see the introduction thread.