It looks like someone has finally come up with a way to clinically diagnose Parkinson's Disease while the patient is still alive. The FDA has approved "DaTscan", an imaging technique which can show abnormalities in the brain which are indicative of Parkinson's Disease. The article came from the Michael J Fox Foundation web site (see link on the right side of the page).
Why is this important? For one thing, the clinical trials and studies for Parkinson's research will be a lot more fruitful. Right now, no one can be absolutely sure that the patient in question actually has PD and not some other disorder. Now, the data collected will be of a much higher quality. Also, of course, patients will get appropriate treatment sooner.
Aside from all that, I don't know about anyone else, but I think that one of the worst things is not knowing. You know there's something wrong, but not what it is, or how to go about treating it. Now we'll know. I think this is a very good thing.