One reason why people switch over to Google Voice is the call blocking, customization, and filtering tools that the service provides. Those got a boost today with integration with Google+ Circles. If you go to the new "Groups & Circles" tab in Google Voice's setting menu, you'll now see that you can choose whether calls from each Circle will be sent straight to voicemail or not and you can tell it to screen all calls from a certain group, which lets you listen in on the call before answering. You can even set personalized ringtones and greetings for each group, so when your boss calls he doesn't need to hear that cute message you have set up. You can't change these settings from the mobile apps just yet, so you'll have to use the desktop interface for now.
Of course, this is yet another example of Google force-feeding its new social network to users — so if you haven't taken the plunge, you're going to have to set up an account and make some Circles if you want in on the new functionality. Will it spur any Google+ fence-sitters to make the move?