Facebook can't catch up without changing their model. With G+ you can follow people who aren't your friends or neither your friends' friends or in your network, etc. You add a dude (or gal) to some circle and you'll see their public updates. It might eat somewhat into the Twitter crowd as you can use it for exactly the same purpose (and much more).
Even though it's early, I already think FB is too late to recover. These social networking websites are either niche sites (IE Linkedin) or succeed each other as king of the hill. FB is old now, has privacy issues that are solved by G+, and G+ has enough PR and interest to reach Gladwell's Tipping Point. And Google's engineers are smart enough to make it work and expand the feature set and they already have experience from both Wave and Orkut.
Now we just wait for people to migrate over.