In all previous clear-cut super-bubbles the equity risk premium has been way below its average of 3.7. Currently at 3.3, this valuation measure is not confirming the signal from real equity returns. For the equity risk premium to get into super-bubble territory, real long-term yields would have to jump another150 basis points or more (think 5% nominal yield). Of course, if the global economy collapses (1974 style) then the valuation debate would be academic.
(Link to Jeremy Grantham's Super Bubble note)