There's a court case pending right now brought by Microsoft against three Los Angeles residents, Zvieli Fisher, Ed Fisher, and M. Zvieli, for buying up domains close to Microsoft's. The companies make their money through page views and advertising. The usual deal is a couple of pennies for a page view, and then more on top of that for any advertising that might be on the page. Users usually catch their mistakes pretty quickly and leave, but not always. Sites that pay for the misspelling traffic have been known to do well in more than just the revenues from advertising and page views.
People come by mistake and stay because what they like what they find.
You're probably familiar with the more traditional cybersquatting laws, under which those who buy domains identical to the names of companies or people can lose those domains under trademark law. Here's the hitch. If you wanted to trademark the name MacDonald's, the U.S. government would most likely turn you down because it is too close to McDonald's. There could be consumer confusion. To further the conundrum, a related legal precedent has already been set.