We hear a lot about "causal properties" of materials or "frequency-dependent dielectric constant". But how important are these concepts and what impact will ignoring them have on accurately predicting performance? These real-world effects result in frequency-dependent loss, frequency-dependent characteristic impedance and frequency-dependent propagation speed. So what? In this webinar, we introduce a simple way of describing frequency-dependent properties of conductors and dielectrics and explore their impact on time domain performance, such as TDR response and eye degradation of high-speed serial links. We show how to interpret the behavior of real interconnects and at what bit rate causal properties are important and when they can be ignored. This recorded webinar was originally presented live on Feb 25, 2010.