As far as Garth Turner goes, I would say don't attack the man, attack the message. He may have been very wrong in the past, but I do believe that he is right about the coming (ongoing) real estate decline. I would love to hear someone present a realistic scenario that outlines how real estate will go anywhere but down over the next few years.
To be fair, you are talking about a prediction, and like it or not, the success of past predictions IS a statistical indicator of the likelihood of current predictions being accurate.
As for a realistic scenario, let's use Garth's prediction that to return to the historical mean, another 10-15% drop is required. IF that were 100% accurate and IF that were to happen this year, then the exact same model that is predicting this drop is predicting subsequent years of price increases and the best time to buy would be as soon as the bottom was hit.
Also, don't forget a prediction has to be useful to have any meaning. His warning to sellers was useful in it's day, now it is buyers that need him to give them a heads up... but Garth is an incredibly entertaining writer and has committed to writing daily, whether there is something new to write about or not. Thus, in a sense, he's the opposite side of the coin of HGTV in the boom haydays... if they were real estate porn, he's apocolypse porn. And I think it's very telling that he is still telling people to stay away from real estate, period, even though he himself picked up an investment property that was a power of sale bargain... why isn't he telling people that most real estate is still overpriced but the odd gems are out there? Is it because that message wouldn't play to the audience he has built up that are 100% negative, and that his real purpose is to preach to his flock?
Don't get me wrong, I actually visit greaterfool and read the comments almost daily, although part of the reason is to enjoy how condescending and insulting he can be at the people that ask stupid questions (something I have to put up with while wearing a smile at work), and if I were buying or selling, I would definately think hard about some of the things said there, but I would also do other research... see what is actually moving in my neighborhood and why, look at my budget, etc. After all, if my house today could sell for $300,000, and a dream house in the perfect location were available for $400,000, then waiting for the bottom to hit would save me at most $15,000 (assuming both my current and new house went down that 15%), but that house might not be available then... or alternately, if I miss the bottom, it may actually cost me more to move to my dream location in the long run. Much like some people will pay a premium to have fixed rate security instead of going with a variable rate, others might be willing to pay a premium for a very specific property. I just don't believe there is a single hard and fast rule like Garth does, and while listening to his advice might be the right thing for many people, it also might be the wrong thing for some. We are not all the average, and anyone that tells you he has the solution for everybody is guaranteed to be wrong, because if everyone is a seller, then noone is a buyer, and you need both for a transaction.