I don't think it's a gimmick, althought Nintendo are advertising it as a gimmick. I think it's cool and so do lot's of other people. It's not going to die down; soon every TV will have 3D functionality. To be fair, I haven't ever watched a proper 3D movie. But I do own a 3DS; and I think it's cool. It adds depth, doesn't give me a headache, and it doesn't bother me that you have to hold it in a certain spot - It's a fricken handheld console, where else are you going to hold it.
What I love most about it though is that it's a step forward. No body should be complaining about it. You can't just go from technology point A to technology point Z, skipping everything in between. You work your way up, slowly increasing it.
3D TVs are a big thing. We're going to see a lot of improvements in television over the next... FOREVER. Adding and improving 3D means improving hardware to run it. Then you get to the point where the hardware's so good you add more shit to it. Before long your TV is a fricken super computer. I don't mind at all.