Lol, i've fixed so many systems with the brown tar color. I find windex to be a great cleaner for this. Although I hardly smoke. My ash tray will be filled with cig butts but I'm lucky If I get a drag or two from that one cig. I get to tied into a game and forget about the cig. The only major problems with the cig tar is on monitors. Like last week I cleaned my cluster server's monitor, when I finished cleaning it and turned it on it hurt my eyes, Too bright.
Other then that it doesn't hurt the PC it self. Just makes it look ugly.
To live is to let die