Just yesterday I posted a video blog mentioning the small user base of Google+. And today, comScore published a report saying that Google+ has hit 20 million unique visitors. Granted, that doesn't mean there are 20 million Google+ users, but it's still a solid enough number to see how it stacks up against Facebook.
For the sake of argument, let's assume that Google+ does boast 20 million users. That's a mere 2.7% of Facebook's 750 million users.
More importantly, Facebook's user base is not limited to early adopters like Google+. This is an important distinction, because early adopter usage is not a good indicator of how the general public will embrace a product or service. And if the public doesn't adopt it, then the site will die off once the early adopters flock to their next big thing online.
I'm not saying Google+ can't one day challenge Facebook's supremacy, but it is way too early to tell and it's something that both social media pundits and brands need to bear in mind.