It would appear that they are, and this is, frankly, a good thing.
Obviously, making the limited sharing features that already existed in Facebook but were difficult to find upfront and center, in the same way Google did with Circles, is a direct response to the growth of Plus. What’s also obvious, is that Google will have to continue to roll out new features to keep Plus from going the way of Google Wave. Facebook already has the community, it already has your connections, and now it’s also making the features people love about Plus available just as easily.
Facebook has a ton of advantages over Google in this space, simply because of the user base. Google Plus’ growth has been impressive, but they still don’t compare when it comes to the potential audience, and number of connections available to you, let alone the established history of communication that you already have within the Facebook platform.
Plus has a lot to overcome, can Google be truly innovative enough to sustain the growth they’ve seen when Facebook has the 800lb gorilla of an established, and much larger user community?