Our eyes just aren't tuned to have good depth perception these days, so 3D ends up as a gimmock, because it doesn't really improve anything... it's like an optical illusion at the end of the day. If you look into the distance for example, not far, even just say, to the end of the room your in, about 2-4 metres - well all that stuff is too far away for depth perception. We have to be able to see alternate views of an object, basically see around it somewhat, before we can decipher it's shape and consider it 3D. The principle is all there, the practice is all there, but the implimentation is fricken horrible. I think that our brain starts to dismiss the effect as pointless - we are still looking at a flat shape, that is telling our eyes and brain that it's super-cool 3D, but our brain knows better and just adapts - it probably tries to flatten the whole image to make sense of it. Anytime I watch a 3D movie, I forget it's in 3D within 20 minutes.
But, it might be a better effect, better prospect for games. Because in a game, you are in control, it might be useful to have depth perception in a game, but in a movie it's just an effect. When I play a 3D game, my brain doesn't start to dismiss it. I have been playing Half-Life2 in 3D recently, using a little headset (VR920), it's actually a pretty cool way to play it. I lean my chair back, plug in a 360 controller, and play in 3D, with the controller, and it's pretty cool - I mean cool enough for me to want to play through the whole game like that... and I've played through HL2 a lot of times. The headset I use has 2 seperate screens, so is free from the issues that other systems might have, there's no flickering or colour degredation. Visually things aren't perfect, as people have already said, the issues with blurring etc stop it being too realistic, it's more like looking at a 1/10th scale model than a real environment. I'd probably not want to watch a movie like that, I'd rather watch a movie in 2D - but for first person games that support a controller, well 3D really can add to the experience, it just takes a little effort, maybe a little weed or a couple bottles of beer, but it can definitely provide an experience that is enjoyable and worthwhile.
Expensive though... I mean my headset was about £250, a good 3D monitor is about double the price of a standard one, nVidia 3D goggles can cost £100 or more, and that ski-goggle thing that Notch mentioned yesterday is probably even more expensive.