edit: For those down voting instead of just disagreeing provide a company and their policy. All the companies I've worked at have been the same as Amazon more or less and all my friends have similar employment clauses.
There were no exceptions allowed.
It was considerably more restrictive than any company I've worked at elsewhere.
Yes, most companies have approval processes. They might even be onerous approvals processes. Amazon expressly forbid me from participating in game jams with people who were not in my org.
Worked at microsoft for 2 years, there are the same policies. It was not contractual though. It's just that there were notes broadcasted saying that whenever you discussed with third parties, you should use microsoft tools if possible. Want to meet someone? Send a Bing Maps link, not Google Maps. Want to share a research? Send a Bing Link, not a Google search. etc.
As for the confidentiality clauses, I work in finance, and the rules on IP and personal projects are the same as what you describe.
Yahoo allowed tracing from 2007 till 2011.
Even Amazon employees in CA should be exempt from this policy.
...which is a big problem if you work at Amazon or Google. (Can you think of a single software project that will not intersect any Google project? Are you sure?)
My OSS project is "software development".
My company's main function is "software development".
These days I'm self-employed and renting myself out to large companies, and this has never been an issue. They only care about the work I do for them, not about what I do in private.
Amazon was more aggressive (in my opinion) and much stricter than any other company I've ever worked at.
Edit: I researched a lot of the other tech companies. Here's Google's documentation, for example, which outlines an exception process: https://opensource.google.com/docs/iarc/