I had the same experience in 2010, but in 2011 they made you sign up. I didn't realize the kid had to be present, so I left the hotel early with my daughter, and planned to sign up her 10 year old Uncle too, but couldn't...so he missed out that day (we came back and did it another day with him).
I waited about 30 minutes, as I recall, and it was not a fun wait. But, the show is still worth it.
Another note, if you sign up and it starts to rain around the time of your show, the show will be moved indoors. Don't not show up because you think it's cancelled. My daughter missed out one time because I didn't know that. Just ask a Cast Member if you have questions.