I'm planning to attend for one of the nights, but have not decided which date yet. As the following information taken directly from the Annual Passholder section of disneyland.com indicates, it seems like it will be an event geared for kids, but I'm going anyway. Just the novelty of seeing Mickey and friends dressed for Halloween will be entertaining. Personal speculation: I am guessing the Hollywood & Dine building could be used to stage this type of event.

For kids, the only thing more fun than trick-or-treating at Halloween is trick-or-treating at "Mickey's Halloween Treat," a private costume party in Disney's California Adventure™ park. This not-so-scary celebration lets little ghosts and goblins (and princesses, pirates and superheroes too) join their Disney Character friends for an evening of Halloween fun and games. In addition to collecting candy and surprises at treat stations throughout the park, kids and their families will enjoy lively music, interactive games and special activities. It's Halloween Disney style!
A Spook-tacular Halloween Treat!
Trick-or-treat with your favorite Disney Characters during Mickey's Halloween Treat at Disney's California Adventure™ park!* Dress up for this not-so-scary Halloween party with special activities and "spirited" music. It's a fun-filled night that's light on fright for the entire family.
Purchase your tickets online and save up to 25% while supplies. (At
www.disneyland.com/ap After logging-in, you can find the link inside the "Annual Passholder Special Offers" section.)
Mickey's Halloween Treat information:
Join the fun on the following Fridays and Saturdays in October:
10/21; 10/22; 10/28; 10/29/05.
Trick-or-treat from 7:30 p.m. - 10:30 p.m.
Annual Passholder ticket price is $15 per ticket with parking included.
Additional Information:
Purchase up to 8 tickets per Annual Passholder.
General Public ticket sales begin 9/15/05.
25% discount is off the "day of" ticket price.
* Space is limited and tickets are available while supplies last. Advance purchase savings available with valid Annual Passport until one day prior to event date and may not be combined with other discounts or promotions. Limit eight (8) tickets per Annual Passholder, per event date. Each ticket is valid for admission to the event and parking for one (1) vehicle (larger vehicles may require an additional fee) on the specified event date. Tickets are nonrefundable and may not be sold or transferred for commercial use. Tickets are not valid for theme park admission prior to the hours of the event. All costumes must adhere to any guidelines as determined solely by Disney. Please choose costumes that are not obstructive, offensive, or violent. Guests' eyes must be visible at all times. Offer and event information and activities are subject to restrictions and change without notice. ©Disney