I have this setup and mostly working. The problem with this setup is that Google Voice does not pass DTMF tones so inbound callers cannot navigate our LinuxMCE IVR. We have the same problem when the house calls us with security alerts, etc., we then cannot navigate the through the IVR prompts.
The setup was not overly difficult, but is not free of problems either. The voice quality is good and it is 'mostly' seamless minus a few quirky things like outbound calls being routed to a parking lot where he lot number is announce music is played for a few quick seconds, then finally the call is connected. All in all I would say it is an acceptable solution considering it is completely free inbound and outbound calling anywhere in the US.