There are alot of threads on this subject on chowhound, one of the more interesting replies,
Monosodium Glutamate is used as an added ingredient in all sorts of savory packaged dry goods, including chips (Nacho Cheese and Cool Ranch Doritoes, Sour Cream and Onion Lay's and Ruffles, and the aforementioned Cheetos), rice cracker snack mix, wasabi peas, Rice-a-Roni, Hamburger Helper, Lawry's seasoning packets (tacos, burritoes, enchiladas), dry soup and dip mixes, etc. It is also found in other packaged foods like Ranch Salad Dressing, French Onion Dip, canned soup (Campbell's Cream of Chicken, Beef Stock, etc), cheese flavored and other crackers, processed cheese products, etc.
I didn't realize it was so prevalent.