This might be fine for a home or studio setup, but for live performance - forget it. The reliability of a PC is nowhere near where it has to be for a live performer to rely on. And besides, it is difficult enough to make the audience realize that it is you performing, and not just a karaoke. I would avoid at all costs being seen on stage with a regular computer. Another thing that live musicians think about is portability, and having to connect anything more than a power chord is a hassle (that's why the built-in speakers on the PSR2000 are so appealing to me).

Regards,
Alex