Its a decent investment relative to bonds that yield nothing, there are far worse alternatives like the S&P500, which has a trailing P/E of 23 (mostly due to crash in energy sector) and a forward 12mths P/E of 18.
Investors are being herded into stocks because there are simply no good alternatives out there, I mean the dividend yield of the S&P500 (which is already low as hell) is
higher than the US 10 yr note, and cash yields nothing, what are investors supposed to do?
Unfortunately this is the world we live in right now, financial repression is the only solution to all the debt problems we face now.