There are downsides to informal "no poaching" agreements. After I left one e-company, I applied at another, and later learned I wouldn't be interviewed because of the previous company on my resume. The first company was major client of the second, and they didn't want to have even the appearance of "poaching."
No, the company's representatives did not formally/explicitly say it. My resume just went into a black hole, where I couldn't get a response from anyone.
Later, some colleagues who worked there mentioned (after I'd found a job elsewhere) that it's something of an unspoken policy between the two companies, and was likely the cause of my experience.
