If they're showing it at GC 08 the press haven't been told. This is what Sony has said we will see behind closed doors:
Thursday- Ratchet&Clank: Quest for Booty
- MotorStorm Pacific Rift
- DC Universe Online (game announced at E3) Sony Online
- Infamous
- Heavy Rain: the presentation will be the same as in E3, but there wont be any embargo.
- Killzone 2: there will be exclusive multiplayer hands on in that meeting room (in the booth, there will be single playable code)
Friday:
- LittleBigPlanet
- Resistance 2: there will be exclusive hands on
- Free realms and The Agency (Sony Online games)
- Heavy Rain: the presentation will be the same as in E3, but there wont be any embargo.
- Killzone 2: there will be exclusive multiplayer hands on in that meeting room (in the booth, there will be single playable code)
And normally they add "Unannounced game" on their if they were showing it when we are preparing what games and when to see them.