I've 2-3,000 miles on an indexed 7-speed drive train. I occasionally miss shifts that I'm pretty sure would have worked fine with friction shifting. Also, I can't stay on my biggest cog (28 teeth) when I want it. Sure, that's probably due to my lack of mechanical skill, but my bet is that I could make it work fine with friction shifting. I'll probably go back - 'probably' because I can live with the glitches.
Around here, I never need the 28 cog. In the Spring, I expect to go to the East coast, where I will have to walk up hills without the big cog - maybe even with the big cog - so I'll probably make the change this winter.