KG,
There may be no standard except for the fact that new leaders (or stars if you will) are born each decade and/or after a big crash. We had our share of crashes and new stars born in the 80's and 90's.
These new company's could be the CSCO's, INTC's and MSFT's, of the world that led the 80's or the QCOM's, RMBS's, and JNPR's, and so on that led the 90's. Quite possibly we are seeing new leadership take form for the new millenium right before our very eyes and may not even realize it. These new leaders could be in the form of the EBAY's, ROOM's, EXPE's and BSTE's for the new world.
Then again it could just be irrational exhuberance all over again or the genie has been let out of the bottle for the short to near term due to the downtrodden market of last 2 1/2 years. All I do know is that to sit on the sidelines while this phenomenon may be taking place would be a shame... Must find a way to fit these into ones scheme of things be it for trading or revolving or?