Update:

Nintendo is aware of the many reports coming in regards to StreetPass crashing after European users try to purchase the new DLC games following this mornings Streetpass & 3DS firmware update.

A Nintendo UK spokesperson had this to say to Eurogamer:

"We are aware of some reports of technical difficulties which are occurring and are currently investigating the situation."

Original:

First off let’s start with the latest 3DS Firmware update (Version 6.0.0-11U.) which adds a new feature to save your backup data and some further system stability improvements.

Save Data Backup Feature:

• Users can now back up save data for downloadable versions of Nintendo 3DS software and most Virtual Console games

Improved system stability and usability:

• Further improvements to overall system stability and other minor adjustments have been made to enhance the user experience.

The Streetpass update brings us three new Puzzles that we can start completing, they are:

• New Super Luigi U
• The Legend of Zelda: Skyward Sword
• Xenoblade Chronicles

We also get some visual changes including the touchscreen which now has a menu. The top screen now has four new buttons:

• Shop
• Exchange Booth
• Updates
• Play (new graphic)

Game details:

• StreetPass Squad - Developer: Good-Feel (£4.49 / €4.99)

• StreetPass Garden - Developer: GREZZO (£4.49 / €4.99)

• StreetPass Battle - Developer: Spike Chunsoft (£4.49 / €4.99)

• StreetPass Mansion - Developer: PROPE (£4.49 / €4.99)

However, if you're interested in buying them all then you should purchase the "Combo Pack" (£13.49 / €14.99) which will roughly save you £1.12 on each pack instead.

You will be rewarded with Plaza tickets and Hats when you meet certain requirements in these new games. Here’s a video showing these games in action.

So far the Streetpass update is only available to Japan & Europe.