I don't think he's used it since, but it became his most famous quote. I'm suspecting it will appear in Bartlet's Quotations some day. It has become a well-known name for the situation we see in the stock market. Even though, I should add, Alan Greenspan never came out and said that he believes that there is irrational exuberance. There are other phrases that people use like speculative mania or speculative orgy that are too strong.
Exuberance gets the mood about right.
I think the bubble metaphor, which has been attached to market situations like the one we're in, is somewhat unfortunate, because real world bubbles, like soap bubbles, grow and then pop suddenly and irrevocably. Stock market bubbles, you never know when they're popped. You go through a period when there are more days down than days up for some time. That's what happens. There's always some uncertainty about forecasting, but I would think volatility might stay up for years.