When I judge a show, I've usually got a pretty good idea who the top showmen are going to be before the showmanship contest rolls around - if I'm just judging showmanship, of course that's different. Very rarely is my mind changed by much during the showmanship classes, so the most important thing I can tell you is that I (and most other judges) remember the exhibitors who do a good job all day, and whose cattle look and act like they've had some attention. You can't act like you don't care in the show then come turn it on for showmanship and expect to win. I limit questions to age, weight, breeding status, and their individual feeding program - I agree that knowledge of the industry is important, but if that's the goal you need to have a quiz contest, not a showmanship contest. My showmanship winners will be the ones that get their cattle presented best, the ones I'd want showing my cattle when it's about the cattle.
I'm not big on switching calves for the same reasons others have mentioned - it can be asking for a train wreck, and it takes up alot of time. It's another thing that has never really changed my mind about who needs to win, so I only do it if show management insists.