Originally Posted by -dustin
what drives me absolutely crazy is when rear shifter housing has to be routed on the right-side of the head tube, and front housing on the left side.
You don't have to do it this way if the bike has downtube shifter bosses. You can route the rear (right) shifter housing to the left of the headtube and the front housing to the left, then cross the cables under the downtube to get the operation to the right derailleur.
If the cable stops are headtube mounted you are out of luck.