Google+ (pronounced Google Plus), which is Google's new social networking site meant to compete with Facebook, has had explosive growth, hitting 18 million users after being introduced only three weeks ago. AND, it's not even yet publicly available. It's rolling out gradually via the invitation model, which is how Gmail began its life. I've used it a bit and it's impressive — more intuitive and friendly than Facebook. And if you're one of the lucky ones who's been invited to sign up, Google has now released their free Google+ app. You can read a review on CNET.