I think non-competes must be enforceable in California since I've been slapped with one while working for a CA-based company. That said, I suspect that they're not easily enforceable or frequently enforced.
It seems to me that the idea behind this was not fundamentally price-fixing but eliminating the kind of disruption to projects (and inevitable leakage of ideas and technology) you'd get from having people hopping around from company to company. Price fixing may well have figured into it, but I doubt it was the main reason.
"Veridian does love its money." Veronica (Better Off Ted)
http://online.ceb.com/CalCases/C4/44C4t937.htm