I have a Garry Fisher Marlin with a Shimano Acera shifter and the Alivio rear derailleur. There is a LOT of friction for shifting down (shifting from "high gear" to "low gear") on the rear gear set and I having a lot of trouble diagnosing it. When I removed the chain and disconnected the cable, the neither the derailleur or the shifter seemed to have any friction. However, when the cable is connected, there is friction even without the chain. Trail riding (or anything when you're trying to get from high to low quickly) really sucks when you can't shift and just about break the lever trying to do so. Buying a new derailleur and shifter is not out of the question--whatever it takes to keep the bike moving. It's, of course, much better to be able to fix something--lube or whatever.
I agree with retro but would also add that the rear peice of housing by the rear der also takes alot more wear to the liner inside the housing because of the bend in it. cable is wearing through it quicker than other peices of housing.
I picked up some new housing at the bike shop today. He cut me a piece a couple inches longer, as the stock one seemed a bit short. The guy noticed it was quite kinked at the ends, which should have occured to me as a reason for having so much friction. It's also been through all sorts of water splashadge, rain etc. Should have changed it a long time ago.
Breaking down the shifing sequence is as easy as this. From the shifter through the first cable housing to the break where it fits into the first flange, hold the cable in your hand(after it is removed from the deraileur) and shift and feel for resistance. Then move down the cable until you get to the deraileur. I don't know whether or not you have new cables or whether they are universal or specific to index shifting systems but, this is what I would check. If what you are using are universal cables, rip those bad boys off and throw them away! Jagwire cables with deraileur ferrules could be the answer. Spiral type cable housings cause sloppy shifting, and cable binding. Once you cut those housings, you have to grind down the area where you cut so the cable does not rub. I went through 3 shifter cables with bar end shifters before I did this, yet it is still no guarantee. Just use caution
This is routine maintenance and I don't think there is any danger to be concerned about.
I don't know about standard spiral cable vs what ever the other stuff is, but what I got from the bike shop is spiral cable, which is the same thing that's been on my bike since I got it 5 years ago and never given me any problems. I don’t see any reason to “rip it out.” The reason why I was having the problems was, again, mainly due to kinks in the housing closest to the derailler, which had accumulated from minor crashes on the trail, bike transportation etc. in addition to whatever had resulted from normal wear and water seeping in, which certainly happened over time from ridding though creeks, riding in the rain or wet conditions etc. When I first posted this thread, I had not accurately diagnosed the problem and come to that conclusion.