I've had four ferrets and I just loved them. They do nibble and they can bite fairly hard, but they won't bite hard once they're nice and tame and they're awfully cute. I wouldn't have one with a dog, though. The dog, no matter how well-trained, just can't get over the idea that the ferret is prey. We had the best-trained, most well-behaved dog in the universe when we had our last ferret, and she plagued the poor thing and tried to break into his cage until we had to keep them in separate rooms with a door closed between them, and that wasn't fair to the poor ferret, who loved to explore. They're very curious, so you should baby-proof your house thoroughly if you plan to get one. They chew on electrical cords, for example. They can learn to do tricks and they'll ride around on your shoulders. Peekaboo (that was our ferret's name) would let me drape him around my neck like a fur piece and he'd snuggle up and go to sleep like that. AND a ferret can learn to use a litter box, but until you show it to him again and again, he's going to make his own and keep going to the same spot.
They do have a musky smell, but that never bothered me. I liked the smell, and they're very clean little critters.