On the other hand, e-book readers have found success by doing things laptops can't, like lasting for a week on a charge, being legible in bright sunlight, and being extremely lightweight. I don't see the same happening for movies (laptops are better for movies since you don't have to hold them up) or music (iPhone/Android wins for that).
Also, e-book readers are replacing books, so while you're carrying another device around, it's probably a net reduction in size and weight for most people.
Here's a concept that would sell like hotcakes: Laptop with a dual mode LCD/e-ink 10", touch-sensitive, swivel display that can be held like a tablet, 24hr (or more) battery life, half-inch thick and less than a pound. Not sure if it's technically possible right now, and I'm sure it'd be quite expensive if it is, but when such a device becomes widely affordable, these niche tablet/e-book use-cases would just be part of your laptop.