I don't disagree with no liner and just cable to frame approach. Haven't found any data or study that says the liner makes a difference. There is more friction between similar metals than not, and the sawing action of a cable on the housing is a bit disconcerting to me. I have a couple of bikes that have grooves in the BB from cable wear. At least the liner is replicable!
Note that the clamp on down tube cable guides, like Campagnolo's, are typically chrome plated, which has less friction as compared to bare steel or paint then steel.
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LC_Crank_01, on Flickr[/IMG]