With the recent announcement of the Catalysm alpha, users are warned not to fall victim to phishing scams.
Be aware that if you receive an email inviting you to join the Cataclysm testing cycle then it will most likely be a scam. Cataclysm open beta does not exist as yet.
Do not enter your game username and password into any sites that may link from any email claiming to be an official Blizzard invite to Cataclysm.
If you see a Cataclysm phishing scam then feel free to share your comments on it.