During the fuss of Nintendo World last week, Nintendo opened an official site for the 3DS. The site has a section on hardware with some details that you may or may not have heard about before.
Here are a few points of note:
1. How do you tell a 3DS game apart from a DS or DSi game? Use this as a reference:
I'll also point out that 3DS boxes are slimmer than DS boxes.
2. You can use your DSi and DSi LL AC adapter with the 3DS
3. Outside of 3D support, the 3DS has improved visual quality. You can see this in these Nintendogs comparison shots:
The 3DS shot is on the 3DS's top screen, which supports 800x240 pixels resolution (the top screen is made to output 3D visuals by splitting the 800 horizontal pixels half and half for right and left eyes). The DSi shot is on the DSi's bottom screen, which supports 256x192 pixels resolution.
4. I'm sure you already knew this, but DS software, when played on the 3DS, will not be shown in 3D. Also, the system will not upgrade the quality of visuals for DS games.
5. This is what it looks like when you receive a Mii from another player via Street Pass (where your system receives things from other players while you walk around with it in sleep mode):
This player's name is Suzuka, from Tokyo. The last game played by Suzuka was Nintendogs + cats. You exchanged data 43 minutes prior.
Miis that you've received appear in the Sleep Mode Mii Plaza area, shown here:
6. Different from the DS, Street Pass transfers are handed at the system level -- that is, games can exchange data while your system is in sleep mode even if the game isn't loaded up. If you register 3DS games that you've previously played with the 3DS system, the system can conduct Street Pass transfers simultaneously for up to 12 titles. Street Pass transfers can be regulated via the system's parental controls.
The system-level Street Pass transfers will only work on 3DS games. DS games will still require that the game be loaded up.
7. The Home menu can be brought up in game to pause the game and allow you to look up stuff on the internet, write memos and more before returning back to the game. There are some instances where the Home menu can't be brought up or where some of its functions can't be used, like when the game you're playing is using wireless or the system's camera.