The new update 2.1.0-3U, manly focuses on making the 3DS system more stable and fixing the Ridge Racer freezing problems. Below is how Nintendo describes the update below.

Nintendo 3DS Menu 2.1.0-3U

If you currently have update version 2.0.0-2U, this update provides:

Further improvements to overall system stability and other minor adjustments to enhance user experience

A correction for the screen freeze symptom experienced in the Ridge Racer 3D game

You can receive automatic updates when a wireless internet connection is available. When the download is complete, you will receive a dialog on the HOME Menu detailing the steps to install the update

If you have not completed the update released on June 6, version 2.0.0-2U, this update will add the following new features:

Nintendo eShop
Internet Browser
Transfer functionality to move DSiWare™ from Nintendo DSi™/Nintendo DSi XL™ systems to the Nintendo 3DS™ system
Automatic system updates
Improved stability and performance of the overall system