A few reasons why Knuth considers it as pretty are:
1)The negative of a number is obtained by changing all 1s to -1s and all -1s to 1s;
2)The sign is the sign of it's most significant trit (trinary digit); and
3)Rounding to the nearest integer is identicle to truncating.

Oh, and Cirollo; thanks for the reminder. I had forgotten about the balanced ternary system, but remembered it once I saw the name of it. Perhaps I will do my research on that, I'll wait and see. Update:Hey Cirollo, looks like you beat me to the punch : ) Thanks again!

The 15 year old, sophmore programmer,
Stephen Rawls