Things like non compete agreements, confidentiality agreements, etc should at least get some mention.

In many ways the threat of legal persuasion is stronger than all these technical issues. Any technical solution can be sidestepped or outright broken.

I read recently of a company that maintains one network connected to the world for employees, and another entirely separate intranet without outside connections of any kind just for security. Seems like quite an inconvenience to me but I can see how some data is just too proprietary to leave exposed by any means.