I see about 70 movies in theaters a year, all over the country, and I have never bought a ticket in advance--always in person when I get there. These days, it's usually at the concession stand for weekday matinees, and there's often a kiosk in the lobby where I buy my ticket (and I think at the kiosk there's an option to pick up tickets). At the kiosk and the concession stand, I get a printed ticket.
Generally the only time I go to IMAX is because the movie is only at a science museum. I've never gone to a "regular new release" movie in IMAX. But I regret not paying closer attention because I saw Baz Luhrmann's EPiC: Elvis Presley in Concert the other day, and it was fantastic.
I found out it played for a week in IMAX theaters before moving to regular theaters, and it wasn't on my radar yet during its IMAX run. I think I may have missed a good opportunity.
When they re-released Stop Making Sense, my boyfriend insisted on an IMAX theater--he's picky about sound. I wouldn't have made the effort if he hadn't been going--it was 40 miles each way. But he wanted IMAX, so we made a day of it, and I have to say, it was amazing.
A few weeks later I saw it again in a regular theater, and the second viewing was a great experience, but I could compare and see how IMAX made it better.