"While Google CEO Eric Schmidt was on Apple’s board of directors, the two companies had an agreement not to hire away each other’s workers, a former Google employee with knowledge of such matters has told us.
We have since confirmed this with other ex-Googlers. This was not a written agreement, and was considered non-official, but it was well-known and followed within the recruitment division of Google, we’re told.
...."

Link:
http://www.techcrunch.com/2009/08/07/source-apple-and-google-agreed-not-to-poach-workers/