I bought the Dragonfly (still no headphone amp). Very smooth/laid back sound with a wider soundstage and better bass response than headphone out on my Macbook Air. Possibly a little too smooth for my tastes: it's perfectly fine (and definitely a step up from my Macbook Pro and Mac Mini) but I'm pretty sure that I can hear more detail / texture from headphone out on the Air (as a complete noob, it's not impossible that I could be confusing texture and detail with distortion). I actually prefer the sound from the headphone out. To some extent, I think this is true for both my AKGs and Grados but seems to be especially noticeable with the higher impedance AKGs (Grados ~30 ohm vs. AKG ~ 60 -70 ohm) so perhaps it has more to do with the amplification stage of the Dragonfly (and so potentially improved with a decent amp).
My opinion might change with a good amp (and maybe I've just become familiar with the Macbook's onboard audio). I'm not sure. I might take the Dragonfly back to the dealer...