Most people regard typos as nuisances, just inconsequential mistakes that cause them to lose a second of time hitting the backspace key. But for Google, typos may equal big business, as Benjamin Edelman and Tyler Moore have estimated that they make the search giant $497 million per year.
Edelman and Moore, who both call Harvard their home, coauthored a paper titled "Measuring Typosquatting Perpetrators and Funders." In a blog post summarizing it, they presented several sets of statistics and wrote, "According to our analysis, 57% of typo sites include Google pay-per-click ads."
Then they made a rather more interesting comment regarding the effect of Google's connection: "Combining our observations with financial reports and others' estimates, we conclude that Google's revenue from typosquatting on the top 100,000 sites is $497 million per year."
Also, Google's pretty much the only search engine they point a finger at, since not nearly as many ads from Yahoo and Microsoft appear on typosquatting sites.
Now, it's necessary to mention that Edelman is involved in a lawsuit against Google ("arising out of Google's use of typosquatting domains to display advertising"), so he may not be the least biased person in the world. The numbers he and Moore presented are still stunning if true.
UPDATE: Ben Edelman was good enough to drop by in the comments section, and he wrote, "Surely it's not Google's fault that some people misspell. But our study [shows] that typosquatters register more domains targeting companies in sectors with high PPC prices. That tells us that PPC funding is *causing* and *exacerbating* typosquatting. Without PPC payments, there would be fewer typosquatting registrations -- much less reason for squatters to register these domains. Google's payments put the system in motion; squatters register domains exactly in anticipation of getting paid by Google. Google knows where it's showing ads. (Example: Google shows Expedia ads if you misspell Expedia, but Travelocity ads if you misspell Travelocity!) So it's natural to look to Google for resolution of these problems."