Microsoft just won a temporary injunction preventing a former Microsoft executive (named Kai-Fu Lee) from working for Google on certain products and services. Mr. Lee was previously the 'face of Microsoft"? in China, and Microsoft objected to him playing the same role for Google.
In awarding the injunction, the court ruled that 'Mr. Lee had misled Microsoft about his intention to return to Microsoft following his sabbatical and he continued to have access to Microsoft's proprietary information after he decided to leave Microsoft to join one of its competitors without informing Microsoft."?
However, the court stopped short of prohibiting Mr. Lee from working for Google altogether, provided that Mr. Lee does not use or disclose any of Microsoft's confidential information for Google. The result might have been different if Mr. Lee's contract contained a non-competition agreement (or perhaps a differently worded non-competition agreement).
Executive employment contracts often contain provisions dealing with confidentiality, non-competition and non-solicitation. The enforceability of these provisions varies from jurisdiction to jurisdiction.