It's hard to pinpoint exactly, but there was a time when it became clear that Microsoft's actions as a whole were increasingly getting less and less coordinated. They could say one thing on one event, and another division could say something completely conflicting a week or two later.
Their execution strategy and ability to put the entire company behind it has been sorely lacking for many years, something even Ballmer recognized before announcing he was stepping down.
This is ofcourse 100% subjective and not very scientific, but IMO we are seeing the same trends with Google. They have different divisions saying and doing different things (like here). They have no clear strategy or message about where they're going next.
You have the smudge of partially or completely overlapping platforms like Chrome, ChromeOS and Android. For ages you've had Google talk (IM), Google Voice (and or regular SMS depending on geographic region) and G+. Now they've started looking into consolidation, but it took them years.
Google is fragmenting at their seams with a myriad of platforms and services, and their attempts at putting things back together seems mostly driven by the G+ initiate, a initiate which has faced massive user-criticism due to the way it is being executed.
This feedback, had it been taken to heart, would have led to changes around G+ but so far we've seen none. This is like Microsoft and the whole Metro/Win8 fiasco. They think they're too big to fail and just keep on pushing.
All in all, all those small pieces start to add up. A lot of the things we saw with Microsoft, we're seeing again with Google.