I’ve spent about a week with the Yamaha P70 Digital Piano - now that I’ve had some time to play on the piano (and listen to it on a fairly nice headphones!), I figured I’d add my two cents about this piano coming from a purely classical point of view.
Sound: There are two piano voices on the P70 (on top of electric piano, organ, etc). I tend to play with the first piano voice since the second voice sounds as if I’m playing in an empty room - it has that hollow tone to it which I find a little off-putting. Both voices sound fairly nice around the middle octaves but the lowest octave leaves much to be desired - playing single keys are fine but if you play any chords on the last octave, there seem to be some sort of dissonance between the overtones that makes the chord sound muddy and a bit off. The top end is slightly shriller than I’m used to. However, in typical classical pieces where very top and bottom octaves are rarely reached (and even if they are, they tend to be one-off notes, not chords), the P70 sounds surprisingly nice and life-like. I can reach the limitations of 32 note polyphony by playing extended runs with sustain pedals on… but only if I try - I’ve yet to run into notes cutting off in playing actual pieces.
Key Action: Another thing that I was fairly worried about was the key action - overall, it’s not that bad. I’ve seen pianos with far worse action and after a week of playing, I’m already used to the weights and responses. When I first started playing, it felt as if the keys weren’t returning fast enough (ie, no bounce off the strings of a real piano) but I don’t even feel that anymore. At the store, I preferred Casio Privia Digital Piano’s action so it’s good to know that my fingers are already getting used to the P70’s. The Privia’s sound wasn’t as… rich as the Yamaha’s.
Pedal: Yamaha P70 comes with piddly little pedal that looks like it came from a sewing machine. The pedal that comes in the box is also on-off so half-pedaling is out of the question. Yamaha FC3 pedal supports half pedaling and seems to be of reasonable price so if you’re serious about playing, pick up the pedal while you’re getting the piano.
Build Quality: Sturdy plastic, not much to say. It’s fairly light (~25lb?) and the built-in music stand plastic thing seems a bit cheap but hey, what can you say for $600?
Output: P70 comes with 2 headphone jacks and MIDI ports. No line out, so it’s not really meant for gigging. As a day-to-day practice piano, P70 seems to have everything you need and more.
At the end, what it comes down to is that when I’m playing, Yamaha P70 doesn’t distract me away from playing music. As a $600 entry level digital piano, that’s more than good enough for me. 
