Not a user of one, but play testers have said that it can get very nauseous after short periods of play.
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While the hardware can definitely be blamed for causing nausea (refresh rate isn't high enough, tracking isn't spot on, latency is too high, etc), it's mainly the software that will screw with our easily confused brains. If game developers design VR software well (no player acceleration, no camera overriding, no strafing or yaw-turning, provide a fixed reference point like a cockpit etc.) then you won't spew nearly as much. This is one of the reasons I would recommend waiting. Games need to be created specifically for VR in order to be comfortable for hours at a time.