Looking around my system, I see a new "Nintendo Zone" app for interfacing with "participating locations," to receive special content from certain free wi-fi hotspots. The "3DS Camera" app now has a toggle for video or stills, and -- most unexpected of all -- there are new "accomplishments" (achievements, kind of) in the StreetPass Mii Plaza. A few popped up immediately upon starting the app (above). You can see them all in a list within the Mii Plaza. I have 20 total (!) relating to the number and location of the people I've met.
Other new stuff in the StreetPass Mii Plaza includes a music player for Mii Plaza music, new Find Mii stuff (Find Mii 2 game and lots of new hats, accessible only to those who have all the hats from the first game), new Puzzle Swap puzzles, and even some kind of new SpotPass connectivity, to bring Miis into your Plaza from the internet. I'm not sure how this works yet.
Though the eShop was down all day in preparation for this update, I didn't see anything new there yet -- except for a news item about the 3D video update.