It is extremely easy to learn the art of accurate non-indexed shifting. Unless you are racing in a peleton, indexing brings little added value.

For me, the big arguments in favor of friction shift or a linear-throw indexed shift with a friction option are: 1) near-universal compatibility among mix-and-match components; 2) ability to shift quickly and smoothly across any number of cogs; 3) ease and stability of adjustment. All of my road bikes have no-index shift -- either barcons or downtube levers -- and my mountain bike has 7-speed SunTour XC thumbies, which I have always kept in friction mode. Now that I run an 8-speed Shimano cassette on the mountain bike, friction mode has become mandatory.