I just finished a design of parallel a RGB bus to pump image data into a TFT display. The bus frequency is 25MHz. To prevent crosstalk between the lines i placed ground polygons in between each line on the pcb. I wondered if this might harm the signal integrity due to a higher capacitance to ground of each track. The formular for the capacitance of a simple plate capacitor gives me about 2pF (length: 80mm, 35µ Cu, epsilonR of solder mask = 3.5) so there should be no problem. After all this is just a question about style: is it useful and usual in some cases to place ground polygons between bus lines?