Reversing course last week, Goldman Sachs said it will not offer its wealthiest American clients a chance to buy into the social-networking site Facebook. That controversial decision aside, says James B. Stewart in The Wall Street Journal, the critical question for eventual investors is whether Facebook's business model and technology are truly impossible to replicate, ensuring that "it can extract high profit margins for the foreseeable future." Though it's unclear how Facebook will make money going forward, especially given the "paucity of financial results" it has released, the company's future looks bright. Facebook, says Stewart, is the world's dominant social network, boasts "unrivaled data" on how people use the site, and — because of all the information it gathers — is "a marketer's dream." Here, an excerpt:

"Facebook isn't going to be for everybody. But its potential strikes me as vast, and at this point, largely impervious to competition—not that it can afford to take anything for granted. I'll go way out on a limb and say that I think Facebook is cheap at $50 billion. If it is a natural monopoly, and given that it already ranks as the most-visited site in the U.S., it will someday deserve a valuation closer to Google's, which this week stood at more than $200 billion.

Had I been a qualified Goldman client, I would have been angling for shares and would be hopping mad that chance was taken away. But a public offering, with better disclosure and investor safeguards, may still prove to be the better deal—and one widely available to the rest of us. It depends on how Facebook deploys its new capital and whether other investors embrace my optimistic view between now and 2012, when Facebook has indicated it might go public."

Read the entire article at The Wall Street Journal.