They differ from Furries in the sense that furries want to be the animal, and therians "are" the animal. Often therianthropes feel that they share some part of themselves (mind, soul, etc) with their animal, essentially feeling that their "two halves" are one in the same.
Therianthropes, by definition, do not:
-- enjoy bestiality
-- draw/create "furry porn"
-- wear fursuits
-- have actual, diagnosed mental issues
On the whole, most of them are pretty well-adjusted. Generally, any weres that seems a bit "off" is probably either 1) a troll, 2) 14 years old and not quite understanding what they're getting themselves into or 3) just plain dumb.
Therianthropes do not think they can turn into animals in a physical sense. If you here one speaking of "shifting" or "changing" they are most probably either speaking of mental shifting (where you go into a trance, much like meditation) or dream shifting (dreaming you are an animal). Anyone who says they *can* turn into an animal physically is either crazy (lycanthropy) or they think they're being funny/cool.