While I agree with Cascade 168 in principle, I think both The Fixer, Top506 and myself are saying that it works fine. In my case, both my single and tandem are used in indexed mode (rear, obviously), and both shift crisply up and down. Well, maybe shifts take 0,5 s more when it's -15°C. I ride year round and while I like a well-functioning bike, I am definitely NOT the guy who cleans and degunks a drive train frequently. With two young children at home, I have other things to do!
But it is true that the longer the routing, the more careful one needs to be with cable routing. Make sure the bends are good and that you don't kink the housing when the wheel flops. And if your down tube geometry allows you to cross the cables as shown on BluesDawg bike, do so, because it makes for larger curves and decreases cable resistance. In all cases, I have found that indeed the rearmost curve – from chain stay to derailleur is the most critical one. With compressionless housing (which is very rigid), I find I get the best results if I shape it before I put it in place.