Interconnect capacitance and speed of data transmission?
@clabacchio is correct, transmission line capacitance has a tremendous effect on data transmission rate.

The effect of the capacitance increases with frequency. Take the following example. As you can see due to capacitance the blue output voltage is showing distortion.

  

Now let us increase the signal's frequency:



If this was a communication/data signal it would be useless due to the effect of the transmission line's capacitance to the ground.

A famous example of transmission line capacitance is on the first transatlantic telegraph cable. The transmission speed was so low that a a single character took 2 minutes to transmit and the first message took 17 hours to be sent!

Read more here:
http://en.wikipedia.org/wiki/Transatlantic_telegraph_cable#Communication_speeds
http://en.wikipedia.org/wiki/Transmission_line
http://en.wikipedia.org/wiki/Telegrapher%27s_equations