Yeah, I have to do some touch-up painting on my headtube, where it's been rubbed to bare metal from cable rub.

Definately need some slack. To me, if the cable's don't cross up front, it's too short. I'm also not a fan of running one cable on front, and one on the bakc, since I am a commuter, and have a large light mount on my bars...the only way it can fit is to have both cables come out on front. It can be done cleanly, but it takes a bit of work.