Idealab CEO Bill Gross has predicted that Google+ “will go from 0 to 100,000,000 faster than any other service in history.” It’s a bold prediction, but even he acknowledges just that. His explanation of how he arrived at this prediction is based on the following points:

• “The service is great.”
• The service is “timely.”
• People are engaging with Google+ “like crazy.”
• Rumors have the number of users pegged in the millions, but he says that even if it’s just a million, it might already be the fastest to that number.
• Google is huge.
• The product is “well executed”.
• People are “smitten”

I don’t know how fast the service will get to 100 million, but I have seen some signs over the week or so that I’ve been using Google+ that I think look very promising for Google. I can only speak of my own experience, but I find the navigation bar across Google properties, complete with a bright red notification box for Google+ particularly eye-catching (especially when it has a number in it). I have to click that box to see what the notifications are. That keeps me coming back.

Secondly, I keep getting emails about people adding me. That keeps me coming back.

The mobile app is also key. The notifications coming to my phone keep me coming back. The Instant Upload feature keeps me coming back as well. Right now, this is only on Android. When it launches for iOS, a whole lot more people are going to have a similar experience.

Meanwhile, the service will also do wonders for Google’s Picasa web albums. Before Google+ it had been quite some time since I posted a photo to Picasa, which was once my usual go-to for photo uploading. At some point over time, I simply found myself just sharing to Facebook in most cases.

I will continue to share them to Facebook for the foreseeable future. That’s because most of the people I want to see them are already on Facebook. They’re not on Google+. That may change though. The invites are rolling out frequently. People are already using Google for numerous other things, and they’re going to see those notifications. And even if I’m still sharing to Facebook, Google has still succeeded in bringing me back into the Picasa world, and I’m guessing this will ring true for plenty more people.

Of course, even if Google+ hits 100,000,000 million that will be about a seventh of what Facebook has achieved – granted, Facebook’s own numbers are often greeted with doubt about the activity of users and skepticism about just how many of these are actually unique users.

Gross’ post has about 100 comments, so that certainly speaks to the engagement factor.