Disclosing 911 limitations is important.
After a Houston couple were attacked, and calls through the VoIP providers' 911 service didn't work as the teen making the call had expected, the Texas Attorney General sued.
This sounds like a publicity stunt, but one that can force the consumer voip provider and hopefully the FCC and the carriers managing 911 services into a more-proactive stance. Right now, most VoIP service providers are not allowed to connect directly to the 911 centers in the subscribers' serving areas. This can be corrected with clear regulatory direction (Verizon, for example, doesn't do anything unless they're told by the FCC).