I think I have read that their PE ratio was around 80 at the height of their boom in 1980. In addition their real estate values were way off the charts - they would make the US housing boom look tame in comparison.
The US PE ratio peaked at around 45 in 2000, and their housing is now a lot closer to having reached some sort of bottom. They still have several years of housing inventory to clear as people lose their homes, but they will do this much quicker than the Japanese.
One huge dampener for the US is that real wages have stood still for around 20 years, and people on lower wages have little hope of making progress in the face of cheap imports, outsourcing of sevices overseas, and influx of cheap labour.
