I read the service animal changes from the DOJ, which take effect in March 15, 2011.
The biggest change is that now a service animal must specifically be a dog or (not making this up) a miniature horse. Gone are the days of the "service lizard" or "service ferret." Also, the animal must be on a leash, harness, etc.
Other than that, it's pretty much same as before -- meaning that the example Neil cited (the "dog with a rope") would still be considered a service animal, provided that the owner answered the following two questions appropriately:
1) Is this animal required because of a disability?
2) What work or task has this animal been trained to perform?
Therapy / emotional support / comfort / etc animals are still not allowed under the ADA; but the person could just lie and say that "fluffy can get my medication when he thinks I'm going to have a seizure" and you'd have no way of knowing.
So SOSDD. Personally I think they should just require a note or certification and be done with it; but they're so hung up on people with disabilities not being inconvenienced _in any way_ that they would never require such a thing; even though most service animal users would probably be in favor of presenting at least a note from a doctor. (sigh)