I too rode a moutain bike occasionally for a couple of years- mostly on roads or bike paths. Bought a road bike last spring because I wanted to ride faster and get up the hills easier. I loved it immediately- felt like I was flying effortlessly. I had NO TROUBLE adjusting to the hand positions and only a little adjusting to the shifters. (I still miss the numbers on the shifter that indicate exactly which gear I am in.)
But recently I've been wanting a lightweight hybrid because I want to ride on unpaved surfaces (such as mulch or gravel trails) because my mountain bike is just too heavy and slow but I am not comfortable riding anything but smooth paved surfaces on my road bike.
Good Luck.