I asked a question on Stack Overflow, it got a few up-votes and one answer. I wrote a comment in response to the answer but couldn't submit it because my question had been migrated to Super User (the answer appears to have disappeared in the process).
I'll admit not 100% clear-cut in terms of which site it belonged on, but it would have been nice to have been given the benefit of the doubt rather than having the knee-jerk reaction of the instantaneous migration. I asked it on SO because it related to Java development (seems that some people agreed that it was a reasonable question because they voted it up).
Another example is this question, which seems to me to be clearly directed at programmers even though it relates to hardware. In this case the asker isn't even a Super User user so moving it isn't particularly helpful. Yes, he can become a user, but I don't feel that this hard-line demarcation of topics is constructive.
So, my suggestion for migration etiquette is:
If a question falls into an area of overlap between two sites, leave it on the one that the submitter chose. Migration should be reserved for cases where a question clearly doesn't belong, because otherwise it negatively impacts the user experience (of the asker).