We went on October 4th, 5th, and 6th. The 4th it rained a bit off and on for about four hours. The 5th it RAINED (not just rained) from 8:00 am to 5:00 pm.
Like previous posters have said, rain clears out the park. It was just DD5 and I, and we ended up doing lots of things that we usually overlook. This was her sixth trip to the parks, and it was her first time riding the
Disneyland Railroad, first time on Star Tours, first time to Minnie and Friends, plus we rode Little Mermaid about eight times, and had no wait in the middle of the afternoon for Soarin'. It was great. I'd take another couple days of rain any day.
The best part was, when the rain stopped at 5:00, even a lot of the people who had toughed it out had gone home by then, and many of the outside rides and attractions ended up opening back up. PPF was scheduled to close at 6:00, and I think a lot of people wrote it off for the day. We happened to be in the right place at the right time, and they gave all six of the princesses one more round of 20 minutes each, having two out at a time. The line was pretty much non-existent, and we did Cinderella, Aurora, Tiana, Ariel, Belle, and Tiana in a matter of about 45 minutes! Talk about Pixie Dust!
Tips?
Check the weather before you leave. I didn't do this for this trip, mostly because we were in Vegas for the week before, and because having not had it rain on us ever before, I didn't really even think to.
If it does rain, still go!
If you buy a poncho, spring for the Disney one. They're lots nicer and thicker.
You may be able to avoid buying new shoes using this trick a CM told me about: Ask one of the stores for two plastic shopping bags. Wear one pair of socks, then put the plastic bag over the socks, then layer another pair of socks, and then your shoes. This worked really well for DD on the first day.
On rainy days, characters hang out in the Animation Building in DCA. We saw Goofy, Donald, and Chip and Dale (together) with about five minute waits. We also saw Minnie and Stitch on their way out as we arrived, so I know they were there, but not what their wait times were like.
I was glad I had the Minnie and Friends Breakfast scheduled on the day it ended up being so rainy. We got lots of characters on a day when we wouldn't have had so many because of the rain. So if you think it will rain and like to do the characters, maybe schedule a character meal.
When it's raining, I think it's even more important to go with the flow of your kids. I kept asking DD5 if she wanted to go back to the room, or rest, or sit down, etc. For her, a mid day mini-break in front of the fire at GCH was enough, but if she would have needed to go back to the hotel, that would have been fine too. I can't help it if she's a die-hard just like me, right?
I'd take rain any day at Disneyland. It made it much less stressful to decide what to do when the decision was already narrowed down by what was available and open. It really was the icing on the cake for an already special surprise trip with my little girl!