My mom is allergic to cats and dogs, so my childhood pets were reptile until we discovered that mom is not allergic to ferrets.
We got one when I was about eight years old, which snowballed through various circumstances into my mom running a ferret rescue from our house while I was in high school. I think we had ten or twelve of them in the house at any given time from 1990-96 or so. Mom's license plate was "FERRET" for several years. I know a lot about them.
It is true that they smell. The males are worse than the females, even after you get them descented. Spaying/neutering early mitigates the stink but it never really goes away.
It is easy to train a ferret. They can be taught to use a litter box, to do tricks, to respond to their name, etc.
Early on, we gave them run of the house. They'd seriously get into the smallest little spots (up inside the couch, into the waterproofing drainpipes in the basement) and they liked to steal stuff, especially if it smelled funny (I remember they had a grand old time with those rubber thumb-wrestler toys) or made noise (don't leave plastic grocery bags around or the ferrets will hoard them). When we got a new couch, we tipped the old one up on end and a ton of stuff came falling out. Squeaky toys, rubber balls, half-chewed rawhide sticks...the beasts are like magpies.
When we wanted to round them up, we had a little batter-powered toy that looked like a bunny. We'd turn it on, it did this weird chirping sound, and the ferrets would come a-runnin' because there was a rabbit to kill. They'd grab this thing by the neck and shake the hell out of it because that's what they've been bred to do. Do not get a ferret near something it instinctively wants to hunt, unless you don't mind one of the two parties ending up dead or maimed.
Eventually they all ended up in a huge cage in the garage. We'd get them out every now and then, give them some freedom to run on our screened porch, and clean up when they'd crap in the corner (they'd shit near the litterbox just as often as in it at the end there). As fun as they were as companions and playmates, they aren't reallly lap pets because they're so active, and they haven't had the biting-is-playing instinct bred out of them yet so you'd get a bloody fingertip every now and then especially if you offered yourself up.
My $0.02: They're good pets for certain people. If you have other small creatures around your house (guinea pigs, hamsters, cats, children), don't bring one home. And don't buy them from pet stores or unlicensed breeders. That encourages irresponsible behavior and you get an animal that is more likely to have health problems. I guess that goes for almost any companion animal, but it bears saying.