Anyone familiar with the MTB world is aware of the mystical smooth-shifting properties of XTR cable housing (the housing by itself is shimao part #SIS-SP41). It feels like regular cable housing, costs close to regular cable housing (if bought by the roll), and with the exception of the nifty rubber boots on the ferrules looks like cable housing, looks like regular housing too. Despite outward appearances this stuff shifts smoother and lasts longer than anything else out there (maybe the sealed systems have it in terms of longevity, but not smoothness). I personally don't believe in magic, so I did a little poking around to reveal its secret -- Silicon grease injection (click for big, from here):Shimano injects these puppies full-length with silicon grease, and then the little rubber booties keep it clean inside. In a surprising move for Shimano, they even sell the grease separately so you can revitalize the housing periodically (though I can't imagine it wouldn't just make sense to replace for the amount of work it would be to reinject it).
I'm off to Canada for the weekend to rest my damaged back and damage my healthy liver. Ride on, ride hard, ride with Eric. He'll be lonely.