I think more specifically the bubble is forming in ETF's - basically the S&P 500 index. It's still early, but I noticed over the past couple of years everybody who I talk to about personal finance says "you should definitely be in ETFs" for a number of reasons. Generally I agree with the reasons, but whenever everybody says the same thing ("gotta be in tech", "gotta be in real estate", "gotta be in tulips"), it doesn't end well. I think it's time to start paying attention.
Anyone know where to get valuation metrics on S&P 500 vs. non S&P 500 in aggregate? I'd be interested in the relative ratios like P/E, P/B, etc.