I've taken classes locally (bring your own machine) and at quilt shows (machines are provided). Most were a very happy productive experience.
The quilt show instructors would spend a quick few minutes demo-ing how to thread the machine, how to set the tension, etc.
However, my most frustrating experience was a local class taught by an out of state instructor who was staying with one of the students: she and three of the students were a clique! The instructor spent most of her time talking with the clique and gave very little help to those of us who had a question: getting her attention was almost impossible.
*LOL* In another class (one of the peeps from above) had a new machine. The instructor spent most of the time teaching her how to use her machine: it was a quilt making class. One of the students hadn't bought her fabric yet: she spent half the day shopping and the rest cutting the pieces we were to bring to class already cut.
Sigh.
Nevertheless, I still take classes because they are almost always fun and I always learn something new.