All the progress you make in the beta is saved for the when the retail version is released, right?
I've never played a beta where that happens, usually everything is reset.
You do get some rewards for playing according to ND's FAQ:
Will my Beta progress or unlocks carry over to the final game?
No, what happens in the Uncharted 3 Multiplayer Beta stays in the Beta, however weâ€™ve lined up some killer rewards for the retail version of Uncharted 3 if you keep playing in the Beta:
Download the Uncharted 3 Beta and receive the exclusive UNCHARTED 3 PSN Beta Tester Avatar!
Complete 10 matches in every mode of Competitive Multiplayer and receive the Exclusive Beta Decal Pack 1!
Complete 5 matches in every mode of Co-operative Multiplayer and receive the Exclusive Beta Decal Pack 2!
Complete 4 Treasure Sets and receive the Treasure Hunter's Starter Pack!
Rank up to level 25 in the Beta and receive a handsome reward of in-game cash on day one!