As of this evening the US will be the first to recieve the 3DS firmware update. Once you update your system you will be able to download a free "ExciteBike 3D" game and a "Pokedex 3D" game/application from the eshop. you will also be able to transfer most of your game from your DSi to your 3DS.
The update for the rest of the world will be early Tuesday morning on the 7th of June.
The update will also bring the 3ds' web browser on line. The web browser will allow 3d web sites to be full veiwable as well but will not have flash. It is believed but not confirmed to have HTML5 over flash.