(I'm another who got dropped into a "poor for me" role. I waited too long to think about transferring. The site director said that I shouldn't have made that mistake. A co-worker on the same team who was in a similar situation at an earlier stage, on my advice, proceeded to begin his transfer immediately. He had a much better experience.)
where would such a negative perf come from? And what is that sort of record's nature? Is there any managers here who could clarify how this whole shebang works?
Then there's a semi-annual Perfolympics in March and September, which is peer-review driven (engineers drop everything for about 2 weeks to write reviews) but has all sorts of boondoggles that are easy to abuse. For example, there's unsolicited feedback and even manager-only feedback that you don't see. Google routinely has to pay out settlements because of aftermath of this system. If you work in technology, chances are that you know a couple people who've collected six-figure settlements because of things said about them in the Perf system. Needless to say, this only gives Google further incentive toward secrecy.
Also, Perv really is a "permanent record". A bad Perf will block you from getting promotions and transfers 5 years later.
Google is nothing if not abusive with data, although in this case, I'm hesitant to call that deeply subjective garbage "data".
There is no forced curve. One of your "Perfolympics" is actually optional. Perf is technically a permanent record, but promotion committees will rarely look back beyond one or two cycles (e.g. up to a year). Five years is nonsense.
In the end, if a team at google in need of my specific skills (cue obligatory Liam Neeson schtick) recruited me, I'd happily go back. I don't expect that to happen, and in fact, the one project that remotely resembled something I'd want to do there got deprecated.
Life goes on...
What's amazing to me is that employees don't know their rights. If your manager deliberately interferes with your work performance, that's illegal (harassment law). If a company allows transfer, then exploration of internal opportunities is part of the job. A manager who makes transfer impossible through negative reviews is interfering with work performance and therefore breaking the law. (That, by the way, is why "calibration" happens in secret.)
I'd love to see this turn into a huge class action lawsuit against every company (including Google) that does that shit. Serves the fuckers right.
From reading these comments in this thread, it seems that this score is used to evaluate whether to allow the said employee to transfer.
Now, a manager has incentive to keep the best people in his/her team. Is this 3.0-3.1 score something they do so that a good programmer but is somehow "bored" with the crappy work (and face it, there is always crappy work) don't try to all leave?
IF that is the case, then there is something wrong.
HR won't stop transfer with a 3.0-3.1, especially if those are more than a year in the past, but no one will want you. It's the standard ill of closed-allocation shops. When projects compete for people, the result is better projects. When people compete for projects, the result is worse people.
Captivity is the most common reason for bad perf. Second place is plain old punishment for things that are political in nature. In third place is "storying", which is when a manager gives bad reviews (and often projects with low visibility and no hope of success) to a good employee to bring him within an inch of his life, puts him through a PIP, and then starts giving him more reasonable scores. The manager gets a story about "rescuing" an "underperformer" and looks like a good boss, but the employee is lucky to transition into the company's lower-middle class, because no one wants a guy who was put on a PIP 5 years ago (having stayed with the company, while under the PIP, reflects on him worse than the PIP itself). The fourth-place cause of bad performance reviews is when the manager takes out someone he fears might be better than him.
Somewhere about #13 on that list is actual low performance, because 95+% of real underperformers are so good at underperforming as to be political wizards (they have a lifetime's worth of experience playing politics, since they can't rely on ability) and never end up on the Perf list.
Others who have run into problems and left might be outliers, but it's difficult to come to a solid conclusion based on anecdotes. People who have bad experiences will have stronger feelings and bring up their experiences whenever possible (E.g. michaelochurch who complains about Google every chance he gets) while those who have good experiences like myself don't mention it as much. I only mentioned my case because it was a counterexample to varelse's case, and this is probably true of many others who have had good experiences and don't bother talking about it.
Just remember that the plural of anecdote isn't data, and negative anecdotes tend to suffer from selection bias because they have a greater emotional impact upon the person.