I have 7-speed Sora shifters on my road bike, and it has thumb shifters. The left thumb shifter downshifts the chainring, and the right thumb shifter upshifts the rear cog.
I have XXL hands so I can of crane my thumb up to reach the thumb shifters while in the drops, but it's not the most comfortable thing in the world. I figure that somebody with smaller hands might not be able to do that.
When riding on the hoods I really like the position of the thumb shifters.