I played with a 3ds today, the 3d effect was as expected, it adds depth and doesn't really pop out. You have to look at the screen dead on and after a second or two you see the full effect. I also played that flying game where you have to fly through a bunch of rings. Your plane was the closes object to you, everything else seemed further away. This is really not how I want to play a game, it seems like you can't move your head or the 3d effect will go away. After about 2 minutes of playing I stopped, and it didn't take long for my eyes to feel rather uncomfortable, and they still are now, hours later.
I will probably only use the 3d for some short videos and taking pictures, like I said in another post, to me it's all just extra gravy, I am buying the phone for the speed, not the 3d.