Good thread Al. I visited San Diego Seaworld in 2006, and the number of shows that are put on daily is staggering. The 17 minute killer whale show, the dolphin and pilot whale display, the sea lion, otter and walrus "comedy"...it was overkill and more circus-like than the majority of zoos. Having said that, there were also decent shark, sea otter and manatee exhibits that left me conflicted about the overall experience. At 1,000 acres and with many exotic species it is a must-visit, but the theme park atmosphere is a tad grating.
Often shows can be effective for specific animals, such as seals and sea lions. If they perform a few modest tricks (no diving through flaming hoops nonsense!) then the public can see them getting their teeth cleaned, lifting their flippers for vet care, and various other commands that aren't putting the animals into compromising conditions.
Elephant shows in many zoos are usually far too commercialized, especially with the massive mammals standing on one leg or pulling themselves onto enormous chairs. Big cat feeding in zoos is tremendously popular, as are the raptor shows that are frequently showcased at many wildlife parks.