14 DAY TRIAL // If you think Google+'s huge growth is astonishing - even if you go by the official word, there are millions of users already - you can blame the fact that Google has enabled the invitations system again for the surge in the past couple of days.
Shortly after it launched, the demand was so high, that Google had to disable invitations to keep numbers manageable. The company wanted to roll out the service to a few users to see what works and what doesn't, before making it available to all.
But the ones that did get in liked what they saw and hype grew fast. Everyone wanted to have a Google+ profile and Google had to increase the artificial scarcity.
Even so, plenty of people did get in, many through the email notification work-around. If you already had a Google+ account and you shared something with the specific email of non-Google+ users, they were allowed to sign up as well.
But Google shut down this avenue for a period. It enabled invitations sporadically as well. A couple of days ago or so, users noticed that the "Invite people to join Google+" feature was enabled on everyone's profile pages and has remained so since.
Users can send as many invites to whomever they want. And that's exactly what's been happening, the site's user numbers doubled in a few days and are expected to double again, to reach 20 million by the weekend.
Google has said that this is just a testing phase, but it is also said to be moving fast with Google+ not to lose momentum. The consensus is that Google will launch Google+ publicly, enabling anyone to join, by the end of the month.
If the current growth rate keeps up, there could be tens of millions of users by that time. Of course, there is also the risk of people getting over the 'newness' and stop using the site so often. This is why it's crucial for Google to keep users hooked, enabling them to get their friends in is a sure-fire way.