These mugs are of course functional (painted and glazed with non-toxic, food-safe materials) and most of them are, in addition, fun. Think of them as tiny, practical pieces of art.
A moment on microwaving, since a lot of people have asked about that -- while I have been known to put my own ceramics in the microwave, I don't officially recommend it -- microwaving can occasionally (but not always) cause what is called "crazing" which appears as small cracks in the glaze. Why? Glaze cools more quickly than ceramic (which retains heat) and so shrinks at a slower rate than the glaze. This can happen immediately or even years later, and personally I've seen it happen on many of the commercial mugs I own that I put in the microwave often. So, while the glazes I use are safe for use in the microwave (non-toxic/food-safe) the action of the microwave is not often kind to ceramics in the long run.