Okay, well, I've heard a lot from both ends of the spectrum! I had to look at my shifters; they have the Shimano nameplate on them. I have even replaced the rear cable once, and it was pretty easy.
I guess that kind of answers my question, because it tells me that people have tried all kinds of shifters, and they like all kinds. I'm pretty firmly in the twist-grip camp myself, and like bkrownd said, I can keep my hands in the same position that I was riding in to shift.
Now, next question is... who makes the best twist-grip shifters? Doesn't look like Shimano carries them anymore. What I'm looking for is the ability to shift at least nine gears on the cassette, even ten if possible. Plus the triple on the crankset.