Granted, it will never be as fast as native applications, but I think it should at least be usable, especially on Intel Macs where QEMU is not needed.
I can only hope it's a little faster than QEMU, seeing as how you're not emulating an entire OS, just the x86 machine code for one program. Of course, you wouldn't be able to run anything too CPU intensive in it. However, it does have an option to recompile Windows apps for PowerPC. I wish that people hadn't stopped making PC compatability cards for macs. Sun makes them for their UltraSPARC systems, and while most Macs aren't that upgradeable, you could still have an external unit, if possible.