I like the concept of twist shifters, but they do seem to require a little more technique to use than trigger shifters -- especially old or cheap ones. I replaced the Sram SRT-400 grip shifters on my Trek 750 with some ST-EF51 mountain brifters and shifting is now very crisp and precise.

My wife's Trek 7100 has Sram 3.0 grip shifters with a Sram ESP 3.0 rear derailleur (what an X3 is today) and it actually works pretty well as a system. The left shifter, for the front derailleur, is semi-indexed, so it has a number of detents between the 1st, 2nd, and 3rd chain rings, which I like. I haven't used a twist shifter set, besides hers, that I really like. Maybe the 1:1 cable pull on the Sram derailleurs requires less of a twisting effort? Her bike has always shifted very smooth to me.