Created on 12 May 2012
TroubleGirl

Important news for those who downloaded English or German installer before 12th May 2012!!! You'll have to re-download now new digital downloader and go through the process of installation. You won't need to download full game, as long as you follow the instructions which Blizzard published.
The instructions are following:
1. Get the new Diablo III digital downloader using the links below
2.
Point the download save at the same directory as before
3. If you chose the correct directory only 50MB will need to be downloaded to fix your install, otherwise you'll re-download the entire ~7.6GB
Whether you repair your previous install or download the entire game again, it's necessary to use this new downloader to install and play the game when it launches.
New EU English Installer
New EU English Installer (Mac)
New German Installer
New German Installer (Mac)
Don't forget the spread the word around your friends and acquaintances, so you can all enjoy the game from day #1
Source of this news:
eu.battle.net/d3/en/blog/4410912/
Related articles:
Preperations for Diablo III