1.According to the offical information that unluckily,at present,there havn't any DS flash carts can operate on 3DS.yet,Nitendo has created six Nintendo 3DS Augmented Reality cards that come bundled with the new console include Mario, Link, Pikmin, Samus Aran and Kirby.please look following picture:
at following picture :

2. 3DS with a prompt system ,which will tell users to adjust the distant to 25cm x 35cm to protect user from eyestrain.
3. The detail of Nitendo 3DS host system was released.
3DS Detail Function Introduction :


Compared to former Nitendo consoles, 3DS adds a rechargeable pedestal and a SD card slot in its left as well.
3DS System Setting : Initial system setting contains 3D images, system date/time, network Settings and parents protect four aspects .After set,we can enter in 3DS menu experience.
3DS Memu :3DS interface is similar to DSI and Wii, the mainly interface contains Mii square, 3DS camera, music, AR gaming,Graffiti, notebook etc
1) Mii square


Take phones from 3DS build-in camera(with double exteral camera) and you can create unique three-dimensional Mii image by yourself,this imag can be yourself,or your friends,or your relatives.and this imag can be used in on-line games as well.
2) Music : now can support MP3 format,you can apply voice record to adjust the recording content for game, for instance,players can adjust high volume, speed playback speeds, etc. Music also adding the.3ds brush online function.

3) AR games : Requires to use the 3DS AR card (question mark card ) and camera to operate games. By placing this card down on the table and pointing the 3D camera at it, it will magically transform into a tiny 3D dragon or an oasis with targets to shoot.

4)'Graffiti': lets you draw on surfaces with a range of paints, paintbrushes and other special effects like fire. You can then manipulate your drawing with the buttons.
Source :
3DS Official News
3DS Information Available