You should read this http://blogs.valvesoftware.com/econ...nt-structure-fit-into-todays-corporate-world/ (it's the "political economy analysis" by Valve's economist)
I find it interesting that he mentions Valve's employee count "pushing 400". The Valve Employee Handbook that leaked earlier in the year (~March [Edit: And itself is dated 2012]) has the number at less than 300. This implies that in the space of (well) less than a year the company has hired around 100 people.