emlee,
i think the issue here is the same as that for tilt in photos.
a little bit is usually seen as bad, because you can't really tell the intent of the author. is it meant to be a deliberate move? or is it a mistake, an oversight on his part?
dynamic tilts are almost always pronounced in nature - same for keystone distortion here. as kit says, if you don't see a purpose for it, then it shouldn't be there. same for composition, if an element doesn't serve a purpose, then you should move to exclude it.
