I'm sure you've noticed that both 3D Systems Corporation (NYSE:DDD) and Stratasys, Ltd. (NASDAQ:SSYS) tanked last night. The reason, apparently, was this Motley Fool article, according to two separate posts that attempted to make sense out of the steep drop. Does that make sense to you? No? Well, welcome to bubble investing.

For all the hype surrounding this technology, the fact is that no one knows how pervasive it will be, or how soon. Just as importantly, no one knows who will be on top if or when 3-D printing matures. Investors swarm into 3D Systems and Stratasys because they're the only real options in a tiny little pond of public companies. Other companies provide the software, or aren't public yet, or are so small as to be glorified penny stocks. As the technology matures, these companies might be left behind.

This is a familiar occurrence for those who have studied the history of technology, particularly computing technology. We so often compare 3-D printing to the original computing revolution that this brief overview of the industry from our free report, "The Next Trillion Dollar Revolution," seems particularly apt:

[In the 1960s], systems called mainframes ruled the computing world. Mainframes were massive computers that would fill an entire room and specialized in very specific tasks. For the period, they were stunningly powerful and capable machines, but they were also prohibitively expensive. At the peak of their popularity in 1973, only 14,000 mainframes were sold.

Why does that sound familiar? According to Wohlers Associates, 6,494 high-quality professional 3-D printers sold in 2011, up from 6,164 printers the year before. These are the machines that can retail for six figures, take up a lot of space, and are typically used only by industrial concerns that can both afford the high price and provide the technical expertise necessary to make full use of them. Consumers have virtually no use for these costly machines, and they tend to sell slowly. But that hasn't stopped the market from flooding into these two companies, echoing what happened with mainframe makers.