It's notoriously difficult to get precise statistics about adult websites, mostly because the vast majority of the adult industry is privately held and no one's volunteering much information. When they do, it's often with a "wink, wink; nudge nudge" effect that's universally understood within the industry.

Even though it's notoriously biased and imprecise, Alexa can give a fuzzy comparative picture of what's happening. In the mainstream world, Google is an undisputed traffic leader with a steady Alexa rank of 2 and a global reach of 26.5 percent of the Internet's traffic. Most of the traffic (25.9 percent) comes from the U.S., with Chile, Brazil and India being the next largest contributors at slightly less than 4 percent each. Eighty-four percent of sites on the web are slower than Google, but it's a search engine. Its job is to be fast and accurate.

Compare those figures to venerable thumbnail gallery link list The Hun's Yellow Pages. In the days before tube sites, The Hun was a dynamo, attracting, trading and selling traffic at a dizzying pace. Webmasters were willing to sell their souls for just a brief appearance on The Hun's pages. In January, The Hun's Alexa ranking was 3,490, down 943 over the previous three months. It reached only .0525 percent of the traffic on the web, down 14 percent from three months earlier, and the average viewer only visited 1.5 pages on the site. The biggest contributor to its traffic (31.5 percent) was the U.S., followed by the U.K. at 11.4 percent. Alexa called The Hun a "fast" site because it loaded more quickly than 65 percent of the rest of the web … but it's a link list. What's to load?

The sites getting the lion's share of porn traffic these days are the tubes, despite their comparably poor load times. YouPorn was ranked 37 by Alexa in January, climbing 15 since October. It reached 1.52 percent of the world's web traffic, up an astounding 61 percent over October's level. The average user (primarily from the U.S., Germany and France) viewed 12.1 pages on the site even though 63 percent of sites on the web loaded more quickly. Evidently, although they might abandon a slow search engine or link list, a lot of people don't mind waiting for video.

Xtube ranked 184 on Alexa in January, up 71 over three months earlier. It reached 28 percent of the global web population (up 56 percent over October), overwhelmingly from the U.S. The average user viewed 19.5 pages per visit even though 71 percent of the sites on the web were faster.

PornoTube, with an Alexa ranking of 226 (down 27 from October), reached .325 percent of the web's surfers, most of whom came from the U.S., Brazil and Chile. Once there, they viewed an average of 9.8 pages per visit, despite PornoTube's deplorably slow performance: 88 percent of sites on the web loaded more quickly.

What's most remarkable about the tubes is what they do with their traffic. According to Alexa, 99 percent of YouPorn's traffic stays on YouPorn, with only 1 percent abandoning the site for somewhere else. PornoTube typically sends 2 percent of its traffic to VOD.PornoTube.com, a skinned version of parent company AEBN's video-on-demand theaters. According to Alexa, no traffic abandons PornoTube for parts unknown. As for Xtube, only 50 percent of the site's traffic stays within the root domain; 1 percent leaves the site. The other 49 percent is shuttled to a variety of Xtube sub-domains that represent moneymaking potential for the site: VOD, pay-per-view amateur content, live video-chat rooms and other innovations Xtube has devised to feed its bottom line.

With traffic and holding power like that, it looks suspiciously like tubes might be here to stay.