My 3DS doesn't have a 3D function. You see it is a 2DS.

@Lucidium Are you asking this for your new alien game or just curious? :O

When I first got my 3DS I had it on for Mario 3D Land and MK7. Then went through a phase when I left it off. I turned it back on for Luigi's Mansion and I'm so glad I did. The 3D made that game even prettier!

It depends on the game for me...
I think it's entirely unnecessary for a game like Animal Crossing and it doesn't do much for Mario and Luigi either...
The frame rate drop in Pokemon is horrendously distracting...
The ghosting effect in Pilot Wings Resort makes it hard for me to play in 3D...
And I get really bad ghosting in the Chamber of the Sages in OoT3D...

Yes! Its pretty helpful while playing Kirby but most of the time, its a luxury thing rather than mandatory which I still use all the time

I don't use it too often because I just find the gimmick wears off pretty quickly and rather than admire the 3-d I'd rather play the game.

I always use it myself. Playing my 3DS doesn't quite feel the same without it. Plus, Nintendo makes good use of the 3D feature.

I keep it off. It's a pain to keep it in the "sweet spot".

Rarely. Cant stand the sweet spot thing.

Make a Pschiatrist happy...Read this

I use it, but only when I feel like it! ( which rarely happens!)

I take it you also play your games in standard definition to avoid distractions from the pretty HD images?