Having ridden nothing but a stem-shifter equipped bike from 1982 through 2007, I felt that downtube shifting was a bit scarifying when I got a bike with that kind of shifters. After about 100 miles, that feeling went away entirely. After that, I learned to love barcons on my next bike, except for the fact I kept banging my knee on the shifter when doing the standing-on-pedals mash. (The bike was too small for me).

My point is, you'll get used to any system if you use it long enough.