If you pre-order Grand Theft Auto V on the European Playstation Network, you will be able to download the game, right now. The only problem being that you still won't be able to play it until September 17...

As you can see in these images, gamers in Europe have discovered that if they pre-order GTA 5 via the PSN they can start pre-loading it. Basically this is when 99% of the games' required files are downloaded to your device's hard-drive, ready to go. Then when the official launch dates rolls around (September 17 in this case) you need to reconnect to the Playstation Network (or Steam or Origin, for example, if you were on PC) and download a small amount of data that will decrypt and unlock the game for you.