That is a simple chart of recent 30 Yrs S&P 500 P/E.
> Very few people saw the last financial collapse coming
While media points the last financial collapse blame to CDOs, the fundamentals of it was housing prices. May be it is new to many Americans, but for those who have lived and seen through Japan, South Korea, Hong Kong housing prices collapses in the 90s, it was rather obvious. I remember the moment when I mention it in 2005 and 2006, but no one believe market would collapse, the idea of housing prices would fall was literally unheard of.
Now there are concerns of Cooperate Debt reaches new height, which is often the argument of bubble. The trouble is you cant look at cooperate debt alone and judge it. Amazon is 25B in debt, but they have 45B in cash. Apple are 100B in debt, but also ~250B cash. Amazon were issuing at 10 years and yields about 3.2%, for reference US 30 Yr treasuries has been floating at around 2.4 The vast majority of companies are swimming in cash. ( There is less of it now because of buy backs, which is what pushes those stock prices up )
So while the market, and general economy may not be healthy, I argued it isn't in a bubble either.