I hadn't thought of that... I tried flipping the first 7 bits of google and got woogle, ooogle, coogle, eoogle - which are all registered. I don't think it would be that hard to write a bit-flip miner though. It wouldn't surprise me if sites other than the biggest (maybe ycombinator.com, techcrunch.com, makezine.com) have bit flipped versions avilable. I guess it would be more likely with longer domain names too.

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.