Why are some circuit traces squiggly?

"Squiggly Traces" are actually know as Serpentine Traces. These wires are often used to make traces the same length. In high speed signaling, especially when using differential signaling ( http://en.wikipedia.org/wiki/Differential_signaling ). Differential signaling requires the signals arrive at the same time. Take a look at this Sparkfun Forum talking about what they are with a example picture: http://forum.sparkfun.com/viewtopic.php?f=20&t=29396