It's been said that the most dangerous words in investing are "This time is different." But with the Dow near record levels and the S&P flirting with 1,500, some are considering today's activity "different" from previous highs.

Charles Payne -- editor of Wall Street Commentaries and a regular financial commentator on Fox Business news -- along with analyst Conley Turner explain, "We began today's session at records levels, propelled by a winning streak that has not been witnessed before by most people alive today."

Indeed, he notes that since 1897, we have only seen a similar winning streak in the Dow on two occasions. These years, he notes, were 1927 and 1929. He states, "With that fact, if history is any guide, then there will eventually be some consolidating of gains in the near future. Nonetheless, the current positive trend is secular in nature, and nothing short of a financial accident is likely to cause a reversal."

"The momo crowd is at it again," says Toby Smith. The editor of ChangeWave Investing and panelist on Fox & Friends explains, "Momentum buying (or momo investing) strategies always tend to bid the price of the stock up as it goes higher."

But once the stock starts to sell off, he notes, "sell triggers are pulled and the momo players begin serious selling -- and that selling feeds on itself." But for those not caught up in the momentum craze, he adds, "For us, this just presents a great buying opportunity."

In his view, one such situation in which momentum-selling has created a buying opportunity is Sigma Designs (NASDAQ: SIGM), a maker of processors for markets such as high-def and Internet protocol TVs.

He notes that in Sigma's case, there were two primary factors that caused momo investors to sell. First, he notes, the company recently brought out 'limited' financial results for fiscal fourth-quarter and full-year 2007, ending February 3.

He explains, "SIGM's quarterly revenue was up 197% to $31.2 million, from $10.5 million in the year-ago period; for the year, revenue grew 174% to $91.2 million, from $33.3 million in fiscal 2006.

"But amidst the good news was word of a delayed announcement of further financial results pending the completion of a review of Sigma's stock-option-granting practices." That, he says, was "strike one."