Search Engine Land had an interesting post about question and answer sites today that linked to a thorough reviewfrom MIT Technology Review of six of these sites. Yahoo! Answers was the clear winner, which is can partly be attributed to its sheer volume of users. I created a custom category of the six sites mentioned in the post, and found that for the week ending 12/23/06, the market share of visits to Yahoo! Answers was 47X greater than the share of visits to its nearest competitor, Answerbag. Two of its competitors, Askville and Yedda, were in the gray, meaning we don’t have statistically significant data on them. This is the network effect in action, and the Technology Review article demonstrates it – the reviewer found more and better answers to his questions on Yahoo! Answers because of the volume of users on the site.

A few other facts in the Hitwise data on Yahoo! Answers:

• For the week ending 12/23/06, it ranked as the 100th most visited domain among the 500,000+ websites tracked by Hitwise. It ranked as the #2 site in the Education – Reference category, receiving about 1/5 of the share of visits to the #1 site, Wikipedia.

• Slightly more than half (52%) of visitors to Yahoo! Answers were female for the four weeks ending 12/23/06. 22% were between 18 and 24, slightly less than Wikipedia’s 27% of 18-24 year olds.

• Yahoo! Answers received 53% of its traffic from search engines for the week ending 12/23/06. This was almost evenly split between Yahoo! Search, with 28% of upstream traffic, and Google, with 23% of upstream traffic. This means that Google is indexing Yahoo! Answers content, and is probably almost as effective at driving traffic as Yahoo! placement of Answers content on the bottom of the search page.

• Like most Web 2.0 sites, Yahoo! Answers is optimized for the long tail, and the search terms driving traffic to the site reflect this. In the four-week period ending 12/23/06, Hitwise captured 42,087 search terms sending visits to Yahoo! Answers. The leading term ‘yahoo answers’ only captured 0.59% of the volume of its searches. In comparison, Wikipedia, another long tail site, received 3% of its search term volume from its leading navigational terms. Here are some of the terms that drove traffic to Yahoo! Answers in the past 4 weeks: ‘smith sisters murdered anonymously,’ ‘dealing with regrets from the past,’ and ‘christmas party games.’