Gr. One of those days where I should probably just stay at home.… - Blather, Rinse, Repeat
I've got to say, though, the ambigram/inversion thing was really just a result of playing around with it until something clicked. I've tried doing other words and haven't been as lucky - rotating or reflecting other words isn't easy to do.
I understand that Scott Kim has a freakish talent for things like this. A friend of mine designed a computer game called "Asheron's Call" and bumped into Scott at a conference. Scott was - on the spot - able to create a fancy calligraphic inversion of "Asheron's Call". Neat trick to be able to do at parties.