The "flat structure" at Valve reminds me of the"unlimited vacation" policy at Netflix. It sounds liberating, but also offers the potential for employees to be judged by rules that are no longer clearly spelled out.
"Unlimited PTO" Is a hallmark of most tech companies. And yeah, it's total bullshit. Give me my 4 weeks a year and let me take them without any judgement, thank you.
It may not be spelled out in the handbook, but it's not that hard to figure out the rules in a company like this. Office politics make or break your career.
It's a great place to work for three or four years if they're doing something you want to learn. You wouldn't want to stay too long, though.