I’ve finally found a little information on how those with double majors have, vs those with single majors, fared after college. At http://web.williams.edu/Mathematics/devadoss/careerpath.html is a depiction of how specific double majors have influenced subsequent career fields for Williams College graduates. (Choose the Double-Major tab. Then put your cursor on an item on the right that corresponds to one of the majors. People who have only that major are on the left where there is just the name of that major. People who have a major in addition to that are on the left where there is the name of THAT major. The job areas are on the right.) Assuming that statistically significant numbers are involved, it’s indicated that adding an economics major to a political studies major, for instance, enhances the odds of working later in the banking/financial sector.
Then, a few paragraphs into http://lesswrong.com/lw/ifo/what_should_a_college_student_do_to_maximize/ there’s: “Should I double-major? There are some earnings statistics here; to summarize, two majors in the same field doesn’t help; a science major plus a humanities major has lower earnings than the science major alone; greatest returns are achieved by pairing a math/science major with an engineering major, which increases earnings “up to 30%” above the math/science major alone. I’d guess these effects are largely not causation, but correlation caused by conscientiousness/ambition causing both double majors and higher earnings.” The link on the word “here” in the second sentence didn’t work for me, so I don’t know what place these findings refer to or how they were arrived at.
When you are in college, college is your world and there is a tendency, of course, to want to make the most of it. However, after it, college deflates in importance, becoming eclipsed by subsequent events. Employers look out from this post-college world. Yes, college degrees are sought in recruits and usually the major field matters a lot, but the academic details subside from the focus. The most important thing by far is experience in doing the kind of work the employer wants done.
When employers have to replace an employee who is leaving, they tend to look for a replacement who has similar credentials. When a business or other organization is expanding, it will carefully identify what it needs to get done and what qualifications suit that work. Where a college major is entailed, it will be a single major that will be visualized. The qualifications for the opening will not be framed in terms of a double major, because double majors are relatively rare, especially, of course, specific combinations - the recruitment would be too slow.
If a double major is really complementary, like IT with business administration, it can be positively perceived. Political science added to IT when pursuing an IT job won’t help (or hurt). If a candidate has two unrelated work-specific degrees (e.g. accountancy and nursing), it can hurt, because hirers in each area would be apt to think the candidate uncertain about commitment and prone to leaving for the other area.
It is still more difficult to see the rationale for a triple major. If I received a resume with three majors, my first thought would be that maybe it’s a lie and, when that got allayed, two conflicting thoughts would be: 1) the person is a hard worker, and 2) the person is perhaps keen about academia but less keen about the almost always less intellectually rich (in my experience) world of work. If they were different, work-specific majors, I would suspect that the person has been terrifically insecure about the job market.