Google's definitely lost their way. Got too big, too fast and didn't preserve the culture.
The biggest an organization can get and hope to have a reasonable chance of not going evil is probably some multiple of Dunbar's number. I think realistically the uppermost limit on it is going to be Dunbar's squared and assuming everyone has really high social skills and no life outside work then it's 250*250 = 62k people. But that only counts if everyone's job is doing nothing more than keeping up with the company's culture; no actual work gets done.
If you assume that you want your people to work while they're at the office then Dunbar's probably goes down quite a bit. Let's use the more reasonable 150 number that's closer to average and let's assume that you only want people to spend about 20% of their time on keeping in tune with everyone around them. That puts your group size at 30 instead of 150 or 250.
Now let's suppose that we organize hierarchically and that the senior execs really do live/eat/sleep/breathe the company. They're professional, high functioning managers, so let's give them the full 250. And then let's suppose that there are group managers who split their time between talking with their group and with senior management.
That gives you 250 groups of 30 people each or 7500 total employees. And in order to keep up with all these groups you've got to have 3-15 execs who are all on the same page and running themselves ragged trying to keep up. If you start adding more levels of management hierarchy you run the risk that as information gets passed down the chain it gets modified slightly or tremendously to serve the interests of any one individual in said chain. And there are too many bosses you have to "go over" to get a reasonable chance of talking to a real decision maker if you think something isn't right, but your direct boss is telling you to do anyhow.
This chart shows that Google cracked 7500 employees before 2007. http://www.statista.com/statistics/273744/number-of-full-tim...
I'd guess that they did between 2002 and 2004. The Google+/youtube integration debacle started in what, 2013? That means it took them a good decade before they really started to do outwardly very unattractive things. That's pretty impressive (or my theory is totally wrong).
Either way, past a certain point more employees are more of a liability than a badge of honor. It just increases the risk you do something stupid because everyone believes they're doing the right thing and there are no lines of communication to correct the misunderstanding, intentional or not.