With the arrival of patch #6, Blizzard has also taken the opportunity to reset the beta:

The beta database has been reset to help test a launch-condition environment. This includes a wipe of characters and identifiers, friends lists, profiles, league placement, and ladder ranks. We thank you for your continued feedback and testing. 

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In the near future, we will be doing a full reset of the beta database. This reset will wipe the following information for all players: 

Due to the amount of people currently participating in the beta, this database reset will allow us to monitor and test conditions similar to a game release (albeit smaller). We want to thank everyone for their patience and continued help and support in testing StarCraft II.

 

Source:
Battle.net - StarCraft II Beta Full Reset Complete