I attended this with my DS8 on Monday. We both enjoyed it but my son was ready to leave at about 35 minutes through the show. I didn't argue with him and felt 45 mins was a tad bit too long. Overall though, I was pleased with the show and enjoyed having seat cushions in Theater of the Stars. Also liked seeing Carl Frederickson from Up! Disney just emailed me a survey. I added the show to "my plans" on MDE so that's how they knew I may have gone to the show. Looks like they are considering offering similar type of performances based on the survey.
We got to the theater with only a few minutes to spare because we park hopped from AK and went on a few rides at DHS before the show started. There were plenty of seats available. I was slightly worried it would be a packed house when we got there but opted to not do a dining package because we had an ADR for 50's Prime Time which wasn't a dining package option. Also I figured the typical theme park guest wouldn't be interested in a live orchestra, as most go to ride the rides.