“Irrational exuberance has unduly escalated asset values, which then become subject to unexpected and prolonged contractions.”

- Alan Greenspan, December 5, 1996

“There is a bubble growing. Investors should be concerned about the risks.” - Cheng Siwei, China's vice-chairman of the Standing Committee of the National People's Congress, January 31, 2007

I wanted to bring up an important point in today's Market Report -- and it all ties back to the two quotes I've listed above.

The first quote, as you know, is Alan Greenspan's famous “irrational exuberance” line that he used to describe the rapidly accelerating U.S. markets in 1996.

This quote offers you such a significant timetable because the Nasdaq, at the time of this quote, was trading for 1,306.

As you very well know, the Nasdaq went on to rally over the next five years AFTER Greenspan warned of a let down, hitting an all-time high just under 6,000 in January of 2,000.

I bring this up because a very similar situation happened today in the Shanghai Composite -- and it's having a big-time effect on some of the most popular China-related plays here in the United States.

As stated earlier above, according to Cheng Siwei, who is the vice-chairman of the standing committee of the National People's Congress, “There is a bubble growing. Investors should be concerned about the risks.” This was his direct quote from an interview with the Financial Times.

On this news, the Shanghai Composite closed down 144 points, or 4.9%, at 2,786.33. And many of these China-related plays that trade on U.S. exchanges are getting hammered today. For example:

Virtually everything is down around 3% across the board.

Now here's what I find interesting…

At the time of his statement, Alan Greenspan was the U.S. Fed chairman.

But Cheng Siwei, who made comments about the Chinese markets, does not have any formal control over China's financial policy.

So his comments, in many ways, are nothing more than his own personal opinion. And to have such a dramatic market effect is overkill, if you ask me.

Heck, if we can learn anything from the Greenspan timeline, it's that bubbles do occur -- eventually.

But the upside run always lasts a lot longer than you'd expect.

That's why today's China-related sell-off could serve as a great buying opportunity.