Tunguska, the ternary computer emulator
acc.umu.se
acc.umu.se
http://en.wikipedia.org/wiki/Setun http://www.computer-museum.ru/english/setun.htm
The high level logic for wanting to build one seems sound, but then when you get into the nuts and bolts of it, binary systems are simpler and use less silicon. However, the kinds of logic gates are really quite fascinating (building the equivalent of a full-adder was really cool if I remember correctly)
Can't seem to find the site that has the logic diagrams, but I recall they were particularly intriguing.