I do know several people who have to avoid it because it often triggers migraines.
You know, I thought this was bullshit but apparently they've linked migraines to a mutation in a gene for a glutamate-triggered potassium ion channel. Can it be stimulated by dietary glutamate? Skepticism is warranted but it seems plausible.
None of my migraines have ever been triggered by MSG, to my knowledge, but I only have one every few years or so. (Auras, photosensitivity, and of course the cranial pain.) I'm sure I have a gene for it, my mom gets them infrequently, too.