I won't speak for anyone else but I've had a Rift dev kit for the past several months and what I've found tends to confirm a lot of my expectations: in applications where your viewpoint matches your physical viewpoint (seated in a chair or walking around a small area that stays in one place while also walking in real life) nausea is pretty much not an issue when there aren't other issues with performance (like if you hardware can't keep up with what you're asking it to render, it will "stutter" as the framerate drops but that's more headache-inducing).

Software like Elite: Dangerous or the tech demo "Sightline: The Chair" work great because your "avatar" is in the same seated position as you are. Once you try to shoehorn VR into a more traditional first-person video game style setup, it gets dodgier. Since you don't have the range necessary to actually walk around that far, people tend to use things like gamepads or the traditional WASD/mouse controls to move around. This can really throw you off because in a game, the mouse or analog stick controls your facing direction but in VR, so does your head. At the same time, in real life, you can face your body in one way and still move your head independently. In VR, it can take some practice to be able to "get" that without feeling nausea. Any time your actual head's motions aren't 1:1 with the view on screen it can get questionable. The closest thing I can think of is the feeling of "the spins" if you've ever had too much to drink and try to lay down. The seeming disconnect between head motion and viewpoint motion throws your balance for a loop.

Then there's the whole forward-backward-left-right thing. If you're sitting in a chair but your on-screen body is running around or jumping or falling your inner ear is telling your brain a different story than your eyes are.

Honestly, this is why I have my issues with some projects and users that feel a traditional FPS-game experience is the holy grail of VR. I can see how it would seem that way at first glance because how much more first person can you get? Still, experiences like Elite or The Chair or even a game like Couch Knights where you're looking around at a virtual "game board" while your surroundings stay in place really do create an amazing sense of immersion and presence.

I think that while gaming will be the early focus due to the existing graphics engines and the fact that many gamers are used to buying high end computers and pricey peripherals, the real innovations will come with the projects that are just now getting started. Stuff like using depth cameras to recreate a 3d "movie" you can look around in or transmitting similar information over networks for 3d telepresence is going to be a much more mainstream and transformative development than playing the vidya games in VR.

The article touched on a point that I'm always reminded of. Those old devices like the Apple Newton or even the more popular successors like the Treos and the PocketPCs were awesome and promising but the smartphone market didn't really take off for several more years because the hardware and software needed to make them polished, fast, and ergonomic didn't exist yet. The Rift is like my old Treo but someday the tech will exist to deliver something more akin to a modern smartphone at equally (relatively) affordable prices for average people.