There are 2 points to address, the 400 million milestone and the activity of the users, obviously Google was late in the social networks arena, and it’s product launch strategy and marketing was wrong, Google plus have not learned from the failed launch experience of Google Wave, they still used the same launch strategy for G+ as they used for Google wave, Gmail and an array of other Google services and products! They did not take in consideration some very simple facts:
–Fact 1: You need friend to have a social network: Google Wave and Google Plus are social networks, that means that if your friends are not on the site you will not bother stay on the site!
-Fact 2: You can not invite prom queens and kings to a party without the rest: Google invites, did not allow anyone to join from the beginning, thus the pioneers joined, found no one on the site so they left, then the others joined, but there was less buzz than the moment Google plus launched, so the numbers of people interested was much lower, and as the first batch, they joined, found no one, or few people they knew and then left!
-Fact3: Give them a reason to have a G+ account: Google is acting slow when it should be acting fast, even though there was a failed marketing and launch process, still Google could have salvaged the launch of G+, they have connected the Youtube channels late, the have connected the Google Apps late, they have syndicated their services late and not enough! All this should have been done at the moment of launching of Google Plus or just after.
To resume, Google plus is not a service that users can be on while their friends are somewhere else, unlike other services like gmail, apps, etc, where users could interact with others using these services, with G+ they can’t they need the other with them on G+, for this social thing to work!
Long term, G+ have a future, even though it is being done late and not enough, but it is being done, Google is connecting the services he offers, and with time it will probably push the integration even more, for example:
integration 1: Access Gmail from your your Google plus account.
integration 2: Access youtube from your Google plus videos.
integration 3: Restructure the blog platforms as Google plus blogs ….
400 million user is more than enough to make any social network work, if Google succeeds in bringing them to the G+ network as active users, then on the long run Google plus can easily replace Facebook, simply because Google plus can offer more than a social network, it also offer the services, while facebook even though it is trying but it fails to offer anything other than social, before facebook there were many other networks like myspace , that also had no major services other than a social network to offer, while google have very popular services that it can restructure around it’s new social service!