Google keeps "encouraging" me to install the Google Hangouts software to replace Google Talk. I've avoided this to ensure I don't screw up my SIP connectivity. But it would be very helpful to have a blog or forum post that advises users of your service on this. I couldn't find such info using your forum and blog search tools.
I've seen several comments on the internets that suggest an emerging issue here. For example:
I currently use GVGW for inbound calls, but place my outbound calls via my web browser, ringing to the Google Talk/SIP Gateway. So I am wondering if that configuration will still be supported.
I don't believe that using Hangouts will have an adverse affect. If anyone else here has used it, please chime in. I'll test it out myself.