I've played several Korg pianos through my years as a musician.
Mainly the SP series. My favorite is the SP-500.

They are pretty nice, they can't take a beating as well as the old school Yamaha tanks (The P-150, P-200 and P-250 omg... I could tell some stories about those..) But sound wise they are quite good. A lot of players here prefer the Roland RD series - but I have always found the Roland pianos a bit... "pop'y", and the Yammies are all about rock'n'roll - the Korgs place nicely in the middle. But the keys on the Yammies still rule imho - I don't know what type they use, but the way they are weighted they play close to a real piano - no they don't feel anything like it - but they play like it. The Korg keys get a bit - sticky after some abuse.

DocZ