I rarely use my rift these days, but I've never experienced any sickness with it. In my experience with all the games and demos, the ones that require walking around tend to make you sick. I suppose it messes with some higher function in your brain. Anything that involves sitting, like Elite or driving games, your brain is usually okay with that. Roller coaster demos are horrible, though.
By rarely using it do you mean you're playing Elite without it? Or just not playing Elite as much and therefore not using it as much?