I've read Peopleware in 2009. It was one of the best book I ever read.
But this book is a little old. I'd like to know, in your opinion, what is and what is not relevant in this book?
It's been a while since I read it, but I don't remember anything in the book that wasn't relevant to someone.
What stood out the most was the discussion of process improvement using CMM and CMMI, and no mention of agile processes (although the second edition was printed in 1999, which is a few years before the Agile Manifesto and Agile development went mainstream). But the book is about people, and people haven't changed that much since the first printing of the book in 1987.
I'm pretty sure these were both in Peopleware...
One slightly irrelevant thing I can recall is the story about a bunch of developers in a classic open-plan office (not even cubes, just a grid of desks) taking wire-cutters to the PA speakers in the ceiling, and stuffing tissue paper into the ancient Bell phones (you know, the ones that weighed about five pounds with an actual dial and an alarm-clock-style clapper inside) so that they weren't so distracting when someone called you. Of course, even this story isn't irrelevant once you view it as a developer team doing what they could to establish a decent work environment.
Also irrelevant today is their defense of actual offices with actual doors and sometimes even actual windows. Of course, it's only irrelevant not because they were wrong but because that battle has been well and truly lost for over two decades now.
An excellent book, as you say, and one I should reread.