With about 3000 miles on my 105 drivetrain (second chain) shifting up and down was a bit sluggish and would sometimes jump a little. After having adjusted and lubed everything I thought it might be time for a new cassette. I decided to properly strip and clean the rear mech, and was suprised to find sideways play in the jockey wheel. Even more suprised to learn that it was supposed to be like this to account for imprecise adjustment of the shifter. I filed about 1mm off the bush, put it all back together and it works perfectly now. Geanted there is wear on the drivetrain, but, why have this feature on the higher end stuff if it causes sloppy changes as wear progresses? I mean I'll happily tweak the adjuster a quarter turn and can do it whilst riding. I can see that it'll help with bikes that aren't used much, or people don't know how to adjust. But cmon, this stuff ain't cheap and why buy new stuff when I don't have to?