I didn't know any yellow badge folks myself, and was ignorant of their existence, just as the article mentions.
But red badges (contractors) are ubiquitous. In one case they fired all the QA contractors and made them reapply for their own jobs -- we're talking about people who had deep knowledge of certain projects, who'd been on certain teams for years, who were valued contributors, people who we didn't want to lose. But because they had a red badge, they were subject to petty whims of bureaucrats from on high, unlike white badges. At least on my team, almost all red badge QA contractors were of Indian origin, and often female.
Now that's not very different from how a normal company works. But Google just made the distinction difficult to ignore since white badges had so many privileges, including, for engineers, the right to reallocate themselves, or to exploit the famous 20% time. Google's image is that they are pioneering a different way of working, with more workplace democracy, but the truth is that these privileges are limited to as few employees as they can get away with.
And of course, the biggest class division has to do with the people who do physical labor and sanitation. I tend to work after hours and I also tend to talk to people even if they're supposed to be "invisible", so I've had conversations with some of the workers. (Ironically, one conversation conducted using Google Translate). That person emptying your wastebasket might be qualified to do nursing back in her home country. Oh, and it might amuse Yahoo employees to know that their recycling program is a complete sham -- everything is emptied into the same trash containers anyway, and the workers are forbidden from taking the cans away to cash in themselves.