Today PS3Blog.net (linked above) has confirmed that the LittleBigPlanet Water Beta codes are being sent out and include exclusive unlockables.
To quote: "As a beta tester for this Beta, you will be rewarded with the Beta Test Vest as a thank you for your participation.
It will also be possible to earn a Beta Bug Blaster Hazmat costume, a prize we give only to those testers who go above and beyond the call of duty to provide us with bugs and feedback, or generally make themselves very useful.
There may also be some creative beta challenges, which will give players another way to win one of these rare and very sought after costumes. These costumes are only available from participation in the beta."
Finally, below is a gameplay video of LittleBigPlanet's Water, Multiplayer Level Creator and new tools courtesy of Bart 013. Enjoy!