I'll give my spin:
The Yamaha is bigger, heavier & more expensive to start with - however it comes with the vocal harmonizer as standard equipment; the Korg is an option. The things that interrest me most about the PA80 are:
1)smaller size
2)Dual inputs for Voice & guitar with effects
3)Dual sequencer - sounds like a neat idea
4)Lower price
5)Expected better handling of polyphony in layering situations, and overall "cooler" rhythm patterns. This has been my opinion for a few years now. Korg was always a little "hipper" than the rest, escpecially in the bass parts. I thought the X1 was terrific also, but there were a few irreconcilable differences in the operating system that I couldn't deal with. So......we wait. Make sure you try them both for quite a while before you decide - these are complex machines.