We've seen Goofy, Daisy, and Chip N Dale. Not all at the same time, but on various visits.
I love it because you actually get a coupon for a free 5x7. When you view your photos later in the day, you do not have to pick the one taken at the Meet N Greet as the free one.
We don't do it often because we usually are not in DCA until later in the day. But the days we do go over there, yes, it's very worth it. There's never a crowd, you get one on one time with a character, and a free picture out of it.