i like to judge by size and importance, this being said, it should be as little as possible, and i mean little, you may want to have a look at some of the "kitchen-like" stuff already in FPSC, for instance, that mug and the wine bottle, see how many polygons TGC used for that, aswell as their texture sizes (ofcourse, dont be afraid to make large textures, then the user can dim them down later, or you can)
i'd probably aim for about 70-100 for a mug, keep in mind the triangles that make up the polygon are important, which is why its best to stay with quads, or map out a clean polygon flow, so you can estimate how many triangles (2 for a quad), if its looking too low for your liking, let the texture do the talking, its very well (and obviously known that some detials are best left to the texture, because they present an almost equal or better amount of detail, which is why we're seing normal maps fly up everywhere nowadays) , you can also smooth the normals for the round effect without wasting memory
