I built a 'bit flip miner' tonight. As expected, every variation of microsoft.com and google.com are registered, but there are many bit flipped versions of ycombinator.com, wordpress.com, and paypal.com (yikes!) are actually available (among others). The best thing would be if the owner of a very busy domain name set up a redirect as I mentioned before (on a domain that would be hard to be a typo), didn't tell anyone, then compared the traffic with the traffic on the real domain.