I would love to read about their hiring process. The handbook says that they look for 'T-shaped' people - people who have a broad range of expertise and a very deep expertise in one area.
And then I explored the bios of people in the company, and most of them are professionals at other companies before working at Valve. (8 years at Midway, 10 years at pixar, 5 years at WETA) In other words, they already had a 'dream job', and Valve is their 'dream space' to do their dream job.
I'm probably going to be over 40 before I even get a decent enough resume to impress Valve.