Typo squatters are a loathsome bunch. They're out to make a lots of money with almost no work on their part. In short, they register domain names that are similar to domain names people are likely to visit, but the domain names they register are based on common typographical errors. When you land on typo squatter's Web site you're either served a huge barrage of advertising or redirected to some other Web site, and in many cases that other Web site is serving "pr0n."
Large corporations and popular smaller outfits are the usual victims of typo squatters and also the victims of TLD squatters -- those people who register the .org, or .net, etc.of your .com domain name if you fail to cover enough bases. These squatters damage reputations and violate intellectual property rights. As it turns out, Google benefits tremendously from this huge trend in get-rich-quick schemes because many squatters use Oingo to serve ad content and Oingo is owned and operated by Google, who also makes megatons of money serving ads via its Adsense program.
You can track down this squatter ilk and possibly drag them into court if you feel the need to recover damages. Microsoft recently released a nifty tool, Strider Typo-Patrol. The tool lets you mine data to figure out who these squatters are. Check it out over at Microsoft Research.