Bitsquatting Windows.com
One rather insidious one I'd never considered prior was that lowercase n is one bit from '.'.  So you can also bitsquat on things like, say, wwwngoogle.com or mailngoogle.com.<p>A researcher brought this to my attention years ago with a set of domains in particular I won't name.  What was most interesting to me is just how frequent bit errors must happen.  According to the research, they'd basically received thousands of emails destined for the correct domain.  Really makes you think.