There are a good number of people using the CGN3 in both Bridge and Gateway mode without any problems. That is not to say that there aren't issues to deal with, as there are. Have a read through my previous posting which summarizes the current state of affairs with the CGN3, and if you have any questions after that, post away:
I use a CGN3 with the 250 Mb/s plan, running in Gateway mode with the 5 Ghz wireless up and running and with an older DLink router set up as an access point on the other side of the house using 2.4 Ghz. Don't have any problems at all.