Celebrities have been key in driving Twitter use by fans, and there's no reason to think it can't have a similar impact on Google+. The service isn't exactly overflowing with celebrities at this point, but there are a few, and that number will likely be growing soon.
Below are some celebs that are currently using Google+. Click any of the images to go to their profiles.
There are probably some more, and if you know of any, feel free to add them in the comments.