Interesting question.
The recruitment policies of many of the companies I have worked for have been rather unimaginative and consisted of recruiting almost exclusively from their competitors.
Not, to my mind, the soundest of policies, it usually means that the recruits bring little with them except perhaps an intimacy with those customers who were clients of the competitors and brought nothing new to the company. Some guys, mostly sales, swapped back and forth a few times and each time gained in salary and position on the deal.
But how did this impact on treatment of employees changing to or from competitors? Incidentally, this is probably the most usual escape route since competitors represent the best match to your current skills set.
Leaving one job to go to a competitor I expected the management to immediately let me go,witness me clear my desk and escort me off the premises.
Instead, they made me work my full notice period and use it to work on a new project which had no real value (as I knew they would not implement it anyway).
There was no attempt to get me to hand over anything to any successor.
Incidentally, they believed I should be working a three month notice period since they had had me working at a management level but since they weren't offering to pay me any more (one reason for leaving), I didn't sign the contract and they had failed to notice this.
The company I went to were only mildly surprised that I had to work my notice but patient.
The company I worked for next was a subsidiary of a major company and managed products from other manufacturers in the group and when one of the manufacturers bought themselves out they wanted me to transfer to them. The company I was working for assumed that this would be the case and had advertised my job even before I had interviewed with the prospective new company. I was not upset by by this and there was no malice in it, just a recognition of the natural order of things and I did indeed transfer. This time, the original employers were happy for me to transfer immediately but for a number of reasons (to do with the 1977 patents act) it was important to me that I worked out my notice.
I have no real dramas to report. I suspect that in most cases the fact that going to the competition is one of the most natural routes for outgoing and incoming employees to take si such that it is only in the most unusual situations that there should be blood letting.....
Except, not me, but a colleague who was summarily yanked back to the Uk from the US (due to politics by others) and promptly got a job back in the US with a competitor. The MD was so badly upset by this he wrote an appalling letter to the guys new employees which, if anyone had believed it should have meant he would "never work again". Fortunately, the new employers laughed it off.
JMW