I've got a P80 and I love it. Great feel, great piano sound.
The sustain pedal thing on the P90 looks interesting though. However, given my financial situation there's no way I'm gonna be forking out for a P90 any time in the forseeable future. I'm way too happy with the P80 to consider that - and there are things higher on the list (e.g. a new guitar, new bass, new amp).
So does it look like the P90 uses the same samples as the P120?
I played the P120 on one occasion in a music shop. Feel was great - like the P80 (I assume as far as feel goes, they're the same) - and some of the sounds it had were definitely superior to the P80. It had a very nice Rhodes sound - very authentic, right down to the distortion when you press harder. Much better than the P80's Rhodes-like electric piano sound. However, I've got the real thing - a Rhodes Stage 73 Mark I - so that's not really an issue to me
The P120 also had a vibes sound, an electric bass, and a few other nice ones. The harpsichord sound on the P120 was also far superior as I recall.
However, IIRC - the P120 has fewer piano sounds? I think it only had 2 (plus variations I guess?) - whereas the P80 has four (plus variations - making 8 in total) - Grand Piano, Classical Piano, Jazz Piano & Rock Piano.
For me, the P80 has exactly what I want - great piano sounds and great action, so it's really not worth upgrading, I don't think.