Started reading short seller message boards. Got deep into the weeds with credit default swaps. Found that you could actually see prices for credit default swaps on markit.com. watched priced for BBB- credit default swaps increase dramatically in early 2007. That was the signal that it was over.
Got back in in early 2012 when the loan rate resets from the housing bubble all tapered off.
Moral of the story: in every bubble the money is coming from somewhere. Figuring out where it is coming from will let you predict the big market turn. If you don't know where it's coming from then you probably shouldn't play with bubbles.