Anyone whose engine was revving in anticipation for tomorrow's Gran Turismo 5 DLC should back off the gas pedal and think about making a pit stop. It's not coming, at least not until next week.
For a game that was in development for 5 years and saw a number of delays, a week long delay for some DLC shouldn't surprise you. You've already waiting almost an entire year after the game's release, what's another week?
Knowing that GT5 fans are hardcore and will likely be pissed, Sony will make up for it by giving everyone a "special bonus" when it does release next week.