A portable PS3...

Game studios will release their new games in 2 formats: BluRay disc and "SD" card. So you use BluRay on PS3 and use "SD" card on NGP.

I think Sony will release a PS3 update to let you sync your save games on your PS3 to this NGP. So when you play a game on PS3 and you want to go out, just save your game and sync it to NGP. Then continue to play on NGP.

Even better is to let you save your game in PS3 to an online server. Then from your NGP, load the game from that online server and continue.