Mergers-and-acquisition activity on the Internet is casting a spotlight on one of the Net's largest forgotten online properties: About.com.The array of content sites, which owner Primedia ( PRM) is reportedly in the process of selling, is one of the most popular sites on the Internet, judging from the number of U.S. users who go to About.com at least once a month. With online advertising growing rapidly after a turn-of-the-century collapse, media companies are trying to increase their exposure to Internet advertising by acquiring online properties. Dow Jones ( DJ), for example, recently bought MarketWatch, and The Washington Post ( WPO) went after Microsoft's ( MSFT) Slate. There's no question that the advertisers are back. Bellwether Yahoo! ( YHOO) reported gross revenue of $1.1 billion for the fourth quarter, up from $664 million one year earlier. With trends like that, it's no surprise that companies reportedly kicking the tires of About.com, according to The New York Times, include New York Times ( NYT) itself, Yahoo!, Google ( GOOG), Time Warner ( TWX) and Ask Jeeves ( ASKJ). A Primedia spokesman declined to comment. About.com, launched in 1997 as The Mining Company, was envisioned as a vehicle for inexpensively building up targeted content on the Internet, against which advertising could be sold on a relatively inexpensive, decentralized basis. Subject matter of interest to Internet users was assembled and updated by a network of experts -- independent contractors who published their work under the unifying artistic direction, editorial supervision and Internet address of About.com. Nowadays, About.com comprises hundreds of subsites devoted to special interests ranging from attention deficit disorder to zoology. In October 2000, Primedia announced the purchase of About.com in a deal that echoed some of the justifications for the announcement earlier that year of the merger of Time Warner and America Online. In each case, a major motivation for the transaction was to marry the content of a traditional media company -- Primedia these days publishes roughly 120 specialty magazines -- with online distribution. "While the AOL and Time-Warner merger announced earlier this year created a mass media powerhouse of new and traditional media, the Primedia and About merger creates the leading model for the integration of traditional and new media niche content and the resulting delivery of targeted marketing vehicles," Primedia's then-CEO Tom Rogers said in a statement when the deal was announced in 2000. The Primedia-About transaction, like the AOL Time Warner deal, didn't quite live up to its advanced billing. But online advertising has grown at About.com in recent months. The company said that online advertising was up $6.4 million in the third quarter of 2004, against a background of $324 million in total revenue for the quarter. But the company had little to say about About.com beyond that on its quarterly conference call with analysts. Bear Stearns estimates that Primedia's online properties amount to 5% to 6% of the company's revenue in its Enthusiast Media segment, which in turn amounted to 57% of Primedia's revenue in the first nine months of 2004. (The company is due to report fourth-quarter results at the end of February.) Traffic to Primedia's sites, primarily About.com, is declining but still impressive. In January 2005, according to comScore Media Metrix, 37.9 million U.S. Internet users visited the site at least once, down from 41.4 million in January 2004. That's enough visitors to make the About.com properties the eighth-most-visited site on the Internet, just behind Ask Jeeves and just ahead of Viacom's ( VIAB) sites. Yet that traffic -- likely boosted by About.com's high placement in search-engine results when users search for general topics such as "pregnancy" or "cooking" -- doesn't generate much relative staying power. According to comScore, visitors to About.com spent an average of 6.8 minutes on the site in January, compared with 25.2 minutes for Ask Jeeves visitors and 24.9 minutes for Viacom users. Visitors to Yahoo! spent 287 minutes on the site, while Time Warner visitors spent 331 minutes on related properties. About.com's combination of high reach with low user involvement -- a site that visitors might like to visit, but not for long -- will pose a challenge to buyers interested in maximizing loyalty to the site.