+1 to everyone else's comments. There is nothing worse than a spinning instructor who has never been on a bike in the real world.
To me, the most annoying (and contraindicated) things are the jumps, hovers, push ups, etc., or anything else that you would never do outside. Go to a functional fitness class if you want to do that.
As one who rarely stands while riding outside, I do stand on the spin bikes. However, I only stand for short bursts, and often times the instructors will have the class standing and riding with very hard resistance for 5+ minutes .
It's bad enough to have to come inside and ride and sometimes the choice between spin class, riding on the trainer, or snow shoeing is not a hard one for me. The snow shoeing will always win, if I have the time.