WSJ had an interesting discussion on whether the bubble was unexpected:
A Factiva search of the top 50 newspapers in the U.S. returns 268 stories referring to a housing or real-estate bubble in 2003. In 2004 that number increases to 369 and in 2005 it swells to 1,608. Going month by month in 2005, there’s a steady increase in “bubble” stories in the first part of the year, coming to a peak in June. ... For policymakers, how widespread knowledge of the housing bubble was matters. It is one thing to say that hardly anybody saw the bubble. It is quite another to say it was generally recognized, yet nobody did anything to stop it and nobody recognized just how bad the fallout from the eventual bust would be.
Note: Google Trends places the peak somewhat later (at around August if I can read the axis correctly) - I used the phrase "housing bubble" rather than "bubble".
It made me wonder: What if the Fed began raising interest rates when the bubble stories peaked?
More interestingly is whether the end of the bubble was foreseen? Using Google Trends I was not able to come up with anything.