It seems a lot of people hear about non-competes being not generally enforceable in California and assume that means it's a nirvana with respect to personal IP/moonlighting/etc. Or even that it means there are never non-competes that will cause a potential employer to walk away, enforceable or not.

Lots of California-based companies have strict policies about ownership of projects that you do on your own time. And there are certainly companies outside of California that don't have non-competes and which have liberal policies about open source contributions.