I have a Ti mug (MSR Titan Cup), but it's mostly due to mild obsessive-compulsive tendencies: it goes with my Titan Kettle. I think I might have taken it with me once, when I first got it, and had cocoa with breakfast. After that, it rarely went with me partly because the mug caused packing problems (couldn't get both it and the Pocket Rocket to store in the Kettle.) The main reason, though, was that I could do everything I needed to do with the kettle alone.

Up until recently, I drank water with my meals, and maybe fixed a kettle of tea with my no-cook lunch or breakfast (or for an evening snack.) Now, I'm learning to cook in the bag for breakfast (oatmeal) and supper (Enertia entree), which lets me brew up a kettle of tea while the food "cooks."

I agree, mugs are mostly redundant nowadays.