Sadly they can't recover what was wiped out but at least progress towards beta rewards "has NOT been lost", although you can't check how far along you are.
Yesterday the studio "started getting reports that some users were logging back into the Uncharted 3 Multiplayer Beta and finding that their progress in the game has been reset." Testers had to re-accept the online beta agreement before logging in.
After they did that they noticed their profile was blank - no money or XP. "We’re actively looking into what caused the issue so we can prevent it from happening in the future," said Naughty Dog. "We know this is particularly worrying for those of you who have been working towards to the Uncharted 3 Beta rewards".
"The GOOD news is that your progress towards those rewards has NOT been lost – we still have all of your detailed play history by game stored safely and ALL games you have played in the past and are playing right now WILL be counted towards your overall progress."
"The BAD news is that we won’t be able to update your profile back to your current level, cash and unlocks. Unfortunately, that means all affected players will not be able to check their progress towards the requirements for the Beta rewards," they continued.
"We won’t be able to update your profile or even look up if you had 1,000 XP or 100,000 XP left before hitting level 25 before the Uncharted 3 Beta ends."
What are the Beta rewards for Uncharted 3 fans?
• Download the Uncharted 3 Beta and receive the exclusive UNCHARTED 3 PSN Beta Tester Avatar!
• Complete 10 matches in every Gametype of Competitive Multiplayer and receive the Exclusive Beta Decal Pack 1!
• Complete 5 matches in every Gametype 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!
They added: "You can still actively work towards meeting the requirements for all of the rewards and, as always, everything you do is helping us work towards a much better experience for when the retail version of Uncharted 3 is released in November."
"After all – finding these kinds of issues early is (thankfully) what a Beta period is for."
Uncharted 3 releases exclusively on PS3 November 1st in the US, 4th in Europe.