We went - I just posted a fairly lengthy report in the "Mickey's Halloween Treat" thread.
Tips...if your kids can stay awake for the entire party, I'd suggest maybe NOT worrying too much about getting treats right away (when the lines at the treat stops are longer), and instead get pictures taken with characters or do some of the kid's crafts or facepainting, or even ride the rides. Last night the treat stops really cleared out after the first two hours, though some of that could have been because of the rain...though the worst rain was in the first hour. There seemed to be lots of treats to be had (with short lines) on the two treat trails at Redwood Creek and Grizzly Rapids.
The "character farewell parade" at the end (it starts 15 minutes before the party ends) was fun - they had all the character and many of the CMs who were in costume form a "parade" around Sunshine Plaza - I missed the beginning, so I don't know where they started from. It was a neat way to see a LOT of different characters.
Hope that helps!