Personally, because of my somewhat terrible eyesight, I will only use 3D momentarily when I want to see something 'pop out' in a game, whether it be Animal Crossing or any other series. I find the 3D to be brilliant of course, but I feel that 'normal' perception is far easier. Perhaps those with better eyesight can joy the 3D to a better reception than I, though, that is just my personal opinion. I am old school, and love to play without it lol It's easier and causes less strain on my eyes.
I turned it on once or twice when I first got it, just to see how it looked.
The 3D feature is something I don't really use that often since I usually move around a lot when I'm playing. I'll occasionally turn it on for cutscenes and whatnot, but since NL doesn't have any any of those (at least ones with a lot of stuff going on), I don't really have a reason to turn it on.
Honestly thought this was a thread for how often you use your 3DS, but I understand now xD
I almost NEVER use the 3D effect. I have never used it for New Leaf so far so I have no idea what it looks like. I used it a little playing Ocarina of Time because the areas were so beautiful I had to see what they looked like in 3D and I was impressed. I usually just turn off the 3D when I accidentally turn it on.
The 3D is a nice feature. I usually don't ever get headaches or anything. I don't use it during the day since it doesn't look that good compared to the colors and tones at night. Switching the 3D on and wearing good headphones is a totally different, but amazing experience when playing New Leaf. Off topic, the way Kazumi Totaka produced the music shows that it's meant to be listened to with headphones; even the hourly tunes most find boring become quite enticing and enjoyable.