There is much evidence that the StarCraft II Beta is going to be released very soon.
The Battle.net support site has added a
section (mostly rather generic, for now) for the SC2 Beta, including info on the
SC2 Beta Client Downloader.
The Beta system requirements were posted, then taken down again, but not before a few fansites got copies of them.
[Update: According to Avarius, these system requirements are not accurate, and were a placeholder that should not have gone up.] See
this article at Starcraft-Source [Update: They were taken down at Blizzard's request.] for the requirements. (I just barely meet the recommended requirements

) They include that the Beta currently only supports Windows (sorry, Mac users), and that these requirements are not final.
A few days ago, some pictures of the SC2 team celebrating (celebrating what? Maybe the impending release of the beta?

)
were released, and on the screen behind them was SC2 with "WELCOME TO STARCRAFT II BETA" visible.
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