A lot of our client contracts include mutual "no poaching" clauses. Obviously we are a lot smaller, but what determines when this is OK and when it's not?
Of course, if you aren't in California you can lock them down with a non-compete, but then again that's why (I think) Silicon Valley has been so consistently and overwhelmingly successful (it's the one absolutely unique advantage it has).
Few are wise enough to realize the advantages of an overall healthy ecosystem, and the giants like Intel, once they became giant, only want that to a limited extent anyway.
(By the by, I'm a fan of the laws allowing people to build their own stuff in their spare time without using company resources).