I totally condone the use of fur if it comes as a byproduct of livestock production -- leather, sheepskin, and rabbit fur are perfectly fine in my book, because they're produced as food. I don't mind taxidermy, though I'm disliking the idea of hunting endangered or vulnerable species.
The production of Farmed fur where the animal is killed for it's fur specifically... that I'm going to say that I don't like so much. Rabbits are fine, of course, because they're produced for meat, not specifically for fur.
Another thing I would completely condone and support is if the animal died of natural causes. I saw a picture a little while back on flickr of a ringtail that had been killed, but it had a lovely tail. Taking the tail or other useable fur in that instance is totally fine in my opinion.
I've got a lovely suede coat that used to be my moms. Were someone to splash me in paint for it, I would be wringing some human necks, I think.
This is a whole new dimension to the subject... but I know at least some groups like PeTA are completely against all use of any animal fiber -- no wool, no cashmere... I find that really odd, since the animal isn't harmed in any way from it. In fact, I know there are people out there that take the FUR THEIR DOG HAS SHED and spin it into a fiber that they knit or crochet or whatever with. I find it extremely odd that someone would find that bad. Cashmere is so niiiiiice, too. It's like I can snuggle my rabbit all the time. x3
Though for those that are picky about fur... careful in buying fake fur sometimes... I know that sometimes tanuki (raccoon dog) fur is produced in China and sold overseas as "fake" fur.