The media have been very critical of Amazon's review process, partially fairly, but mostly not.
At the end of every year, I picked 5-10 people I wanted feedback from- teammates, people I've worked closely with, or people I genuinely wanted to get opinions from. They'd each receive an email that I'd requested their feedback and I'd receive around 10 requests for feedback from everyone who asked for mine. The only mandatory one: everyone reviews their boss.
As well, at any time throughout the year, "Anytime" feedback of an identical nature could be sent in. Usually, I sent these when someone had done something amazing and I worried I'd forget it before review time, or I don't work with them often.
Important to note: I can't ever read feedback given to me. I don't even know if anyone I requested feedback from actually gave it or not.
Each review itself took a lot of time to write, 20 to 60 minutes was normal for me. Everything was asked to be phrased in this way: Situation (what's the background on what happened?), Behavior (what did the person do?), Impact (what was the outcome, effect, etc?). You were expected to give a few good examples and a few bad examples.
At the end of all of this review writing, my manager would read through all of my feedbacks, and compile them into a single overall review with the common themes from many reviews.
Downside: bad managers exist. Here's one person who makes the entire decision and he's the only one reading your reviews. That's a lot of power and you need to trust your manager not to abuse it.
Also, that feedback is anonymous to you. If someone is trying to sabotage you, you'd never know- but your manager would, as they can read who sent it.
Upside: if you're into personal growth, an annual review is candy. Here's an aggregate view of where you need to do better. With a good manager filtering out bullshit and finding the real patterns that matter, you got so much out of this.
On the other hand, it took like 2 days to write reviews, and you'd lose your manager for a week or two while he read and compiled.
Of course, I say all this and should be using past tense: due in large part to the media complaining that Amazonians are encouraged to "rat each other out", and that the feedback system was actually a toxic part of the culture, the company got rid of it all. Now you can only say short, nice things about each other and your manager has even more power that he'll never have to justify.
It was good while it lasted.