We were on the Magic just last week. My son and I got to be in Who wants to be a Mouseketeer (and won!)
Here's how that game worked: Everyone walking through the doors was handed a slip of paper with a number on it. Once the game started, a computer randomly chose a number. If the number belonged to a child, they could bring up a parent (and a parent could bring up a child.) I think during the span of time Mouseketeer took up, there was time for about 6 contestant teams. There were only five questions of increasing difficulty, and two lifelines. When we got through all the questions and won, we got two pins and a glass etching of the show logo. People who weren't able to get through all the questions got two pins and something else I can't remember.
One little tip about something that bothered me a touch (and seeing that the OP is from San Diego, this may be of interest) some of the questions asked are specific to Disney World only, so if you've only been to
Disneyland, you may find yourself at a disadvantage.
It was fun to do and my son was WAY excited about being a contestant and getting that pin!