OSDev.org

This is just amazing, This guy is Debugging an OS from Visual Studio to a Real PC.
VS Start the Slave PC, and then you can use breakpoints,stepping and other debugging features, ON
A REAL PC. I believe it's through PXE, But Not sure,
Anyways here's the Video:
Link: http://www.youtube.com/watch?v=d_1Bup3TR_M

Remote debugging is fairly standard stuff. You can also do it using gdb on Linux or OS X. In essence this is what you are doing when you debug a qemu machine with gdb.