The smooth success of Google+ so far is really a case of third time lucky for Google after previous efforts with Wave and Buzz. New research claims more than 4.7m people in the US alone have joined up.

For the last fortnight since launch, Google+ invites (that work) have been rare as hens’ teeth because Google engineers keep opening and closing the floodgates. Timing is everything. The popularity of the service has inevitably attracted cyber criminals who are issuing their versions of Google+ invites in an effort to lure the unsuspecting.

That said, those that get through don’t seem to look back and it is indeed interesting to say that as well as adoption there is indeed a stickiness to the experience that keeps users coming back. A San Jose Mercury News report over the weekend claims that Google+ has even become a measure of who’s ‘in’ in Silicon Valley. A TechCrunch report over the weekend voiced frustration with the sheer volume of users and resulting posts Silicon Valley luminaries like Robert Scoble have amassed (in his case the count is now 30,000).

Over the weekend, it was reported how Google CEO Eric Schmidt reported that ‘millions’ had signed up so far. New research by Paul Allen, a serial entrepreneur and founder of Ancestry.com, claims that in the US alone there are 4.7m users. Allen used US Census data to estimate the number of users based on all surnames that are used in the US.

Only Google really knows for sure how many users exist so far in the US and the rest of the world but I’m sure there’s a lot of high-fiving going on right now at the Googleplex.

The reasons for its success so far are obvious – it is probably the most elegant software Google has released for mass market uptake (the ability to group friends, family and acquaintances in the graphics friendly Circles and the status updating process are a case in point) and probably the best strategic approach if you think of the black social bar that now runs across most Google sites now. I look forward to seeing this happen with YouTube.

The design of the Google+ pages is pleasant and accessible and, I hate to say it but, it does make Facebook’s existing blue and white design seem jaded and a tad old-fashioned.

This is effectively Google’s third go at social in my eyes. Wave, a kind of take on Twitter’s dynamic messaging system crashed hard on the shore of trying too hard. It was clunky, confusing and hard to use.

Buzz, another attempt at social media messaging integrated into Google’s Gmail system with some really cool location-features, but again it was a fragment of what should have been an over-arching strategy.

My guess is wise minds at Google decided that if social is the future then all its products and services must knit into a company-wide strategy rather than taking the odd stab and seeing what worked.

Google+ is working for Google. It’s a good example of what happens if you stand back from a problem, think it out, put your best minds on the job and embrace it into overall strategy.

So the competitive landscape – who is really threatened by this? I think Facebook is solid enough to hold its own for years yet. My suspicion is the most likely casualty could end up being LinkedIn, because the kind of content and interactions being shared strike me as being professional in nature and context.

Will it take long to catch-up on Facebook? I’m not sure that’s the actual intention. There are many directions this can go in. As a backdrop for a wider cloud computing ecosystem we can all work and live in (think workplace messaging along the lines of Salesforce.com’s Chatter for example) it has potential.

What has impressed me the most is how quickly my social graph within Google+ is building as notifications pile in with new connections after just a week and a half. I’m at a third of my connections on Facebook at this point so this is happening fast.

Indeed, it’s a case of build it (properly) and they will come.