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Dear Mr. Palter:
Covenants not to compete between employees and employers are generally not enforceable in California. There is an exception, however, if someone is selling a business and agrees not to open a competing business, or to work for a competitor after the business is sold.
Confidentiality agreements are, however, enforceable.
Here is an article discussing both: http://www.claysonlaw.com/CM/Articles/articles5.asp.