For what's worth with my limited experience with DPs (I bought a YDP-181 two months ago), I found out:
- The notes do not sustain long enough with the pedal, about 10 secs on middle C, more on the bass notes; this is short of the 15-20 seconds you would get on an upright (for a grand, I have no idea since I don't have one

). It makes your playing appear crisper but it is harder to retain longer chords. PianoTeq (modeled piano software) sustains longer and sounds more realistic than the YDP-181 with the "damper resonance" option.
- The sounds improves quite a bit by connecting the DP to a home speaker system of reasonable quality. But then if the piano is not centered relative to the speakers there is some disconnect between the piano and the sound. This might also be due to the fact that I think you can feel some of the vibrations from the built-in speakers, which by default get automatically disabled when I plug a headset (on the 181 there is no line out, you have to use the headphones out).
- I wish there was a bit more volume on the notes in the treble. Some advanced piano software like PianoTeq (and assuming that you have the "pro" version) allow you to customize every single note to make it louder or quieter, and I think you can even adjust other properties (but I only have the basic version).
- I like the sound better with the headphones than with the built-in speakers.
CG