They are frequently enforceable for some period of time, TBD via expensive court action, via the blue pencil rule, a la:
"The employee non-compete clause shall hold for the greater of:
1- 6 months
2- 12 months
3- 18 months
4- 10 years
5- Until son of the son shall climb Mt Doom and steal the emerald eye from the statue of Xxyctl."
A court then crosses out the single lines that it finds offensive.
What is known to be unenforceable is restrictions on use of general professional skills. The particular IP of the non-compete must be identifiable and recorded (on an ongoing basis as part of a process), rather than vague knowledge of business secrets.
"The employee non-compete clause shall hold for the greater of:
1- 6 months
2- 12 months
3- 18 months
4- 10 years
5- Until son of the son shall climb Mt Doom and steal the emerald eye from the statue of Xxyctl."
A court then crosses out the single lines that it finds offensive.
What is known to be unenforceable is restrictions on use of general professional skills. The particular IP of the non-compete must be identifiable and recorded (on an ongoing basis as part of a process), rather than vague knowledge of business secrets.