Hi My Friend!
You are welcome for the BabyCakes info - I was just super excited you asked me another direct question so I'd have the opportunity to pass the info along to you :-)
You are correct, the September 2011 calendars are now up except for Animal Kingdom. They don't always update all of the calendars at once but they should update it soon so keep checking.
Disney has not yet announced the 2011
Mickey's Not-So-Scary Halloween Party (MNSSHP) dates. The
2010 dates began on Sept 14, 2010 so one would
guess (I don't know for sure) that the dates will begin mid-Sept this year as well. The Disney Parks Blog announced the 2010 MNSSHP &
Mickey's Very Merry Christmas Party dates on May 21, 2010. Hopefully we'll find out around that time this year too if not sooner.
I checked the online September calendar for Magic Kingdom. I do see some dates when the park closes at 7 p.m. (Night of Joy is being held Sept 9th & 10th). On 9-18-11, looks like Extra Magic Hours until 1 a.m. so logically that would indicate that MNSSHP is not being held that evening. I would assume that you're safe but I don't 100% know that since Disney likes to keep us on our toes. As soon as your 180 day window opened up, I'd go ahead & call 407-WDW-DINE & try to make your reservations.
Sending you pixie dust for luck on your ADRs :-) Allison