I take it most of you guys are out in the states?
Iv kept ferrets longer than I've kept fish, i don't know what the breeding is like out there, but in the UK most come from working stock. Family members, friends and myself all keep ferrets, I've kept them both inside and out, and only ever had issues with temperature, during the 34degree summer we had a few years back, which was easily remedied by increasing the amount of water available.
Kept in a hutch/run outside, even coming down to find it buried under a foot of snow, all four were sat in the bedding area happy as Larry.
With regards to diet, there are a few things you should avoid feeding regularly, such as dairy products as it can up set there digestion. Mine live on a diet of fresh rabbit meat (Working ferrets so they catch a fair few), Dry foods, occasional treat of eggs and milk and a great vitamin supplement called ferretvite.
If you are buying them as pets as kits it is very very important to handle them at every opportunity as Conner said they are very social but need regular handling at a young age to get them out of the biting habit, you'll probably find you will end up with bloody fingers somewhere down the line.
Hope this helps