[ShredKazoo]

I think the argument would be that if Google knows that Bing could hire its chief of staff at any time, that will cause Google to invest less in R&D because that R&D could fairly easily be obtained by a competitor.

I assume intellectual property law is sufficient to cover this case in practice though, because Silicon Valley is in California where noncompetes are unenforceable, and Silicon Valley is not exactly known for lack of R&D investment.