Writing systems fascinate me, ever since I was a kid and used to make up pretend alphabets. It was this fascination that has led me to (a) learn Russian, and (b) spend time buggering around with installing non-latin fonts for people in the days when it didn't just happen automagically.
It's also got a lot to do with my interest in lunguages and user interface design.
I've known about the Inca coding system for some time but really didn't know much about it and though that it was just a sophisticated tally system. Then I happened across a posting in Wired about a new model that suggests that the system was really ore complex than that and actually functioned as some sort of symbol based writing system. Doubly intriguing as ost other writing systems have followed the marks on a surface model, be they scratched on ostraka, written on the shinbones or goats or even the good old black marks on white paper.
Couple of other references:
Article (originally from NY Times)
Khipu research site