Well, I'm not near the majors, but my first instinct tells me they would probably ask you about it in an interview for a major. Most important is how you answer. I would think an answer something like this would work well: "I changed jobs in order to better my quality of life and to build more valuable experience in the airline industry. I understand this can be viewed as less-than-loyal, but at this point in my career I'm interested in settling into my position here at [insert airline]. I'm not just doing this job to build time, this is my ultimate goal as an aviation professional, and look forward to staying at [insert airline]."

I'm not sure how helpful this is because it's just speculation - and perhaps a bit too optimistic. Maybe some other guys who are more knowledgeable about the hiring process at the majors can offer some more specific points of view. Interesting question, nonetheless.