The downside is that mug cakes are one of the few things my dishwasher can't quite handle (yes, even with prewash and preheated water). That and certain kinds of very paste-y pesto.

For sure - it basically just creates dried lava in the mug. Probably need to soak it for like a day. I wonder if a couple paper cups would be good, or if the heat that is absorbed and re-radiated by the ceramic mug is critical to baking it properly.