I've been playing in dropped D for longer than I care to remember (perhaps 25 years) and whilst it does have limitations and problems e.g. playing along with tunes when the key changes !! I find it suits me. It's especially effective with a capo on fret 7 (playing in A) giving a nice drone effect. Like everything else it's down to choice. I got very annoyed when someone (not on the folk scene) once commented Why don't you learn to play proper ? I'm comfortable with it and it suits me so what the heck !!