Well, I know I've gotten better veterinary advice online than I got at my own vet's office (a downside to owning "exotic" pets, I guess)... so if I were in a reputable medical forum populated by doctors and fellow patients dealing with the same condition I was seeking advice for, I certainly would.
Would I take the advice of WebmasterWorld members concerning an internet business issue? Absolutely.
It's not as hard to distinguish BS from reality online as some people make it out to be... you just have to use your common sense. ;)