A few weeks ago I had these http://www.competitivecyclist.com/pr...87.2171.0.html installed on my bike.

I was having some shifting issues and though I tried to adjust them I just couldn't get them right. I had thought about getting Shimano 6700 Brifters installed (upgrades are always nice, have 105 now) but the mechanic at the LBS said why not try these cables.
I had read about them but thought they were a little pricey for cables. Well they were less then new brifters so I said lets do it.

My shifting is better than it has ever been. Smooth and precise. Now maybe it could be that "regular" new cables would have solved my problem but it seems these are effortless to shift.
They are a sealed system so they will not get dirt and grime in it anywhere to slow it down. They are a cable within a housing that runs the entire length within the regular housings.
Had the brake cables done too.
Pricey but I am a believer and a happy customer.