Many prognosticators have looked into their crystal balls and made predictions about social media in 2011.

Of course, some of those forecasts could be as shaky as the future of Myspace or as solid as the future of Facebook. We’ll leave it up to you to decide how many of these predictions are tweet-worthy:

• Facebook will top 1 billion worldwide users by the end of 2011, according to Likeable Media. Now, the social media site has more than 600 million users.

• E-mail will enjoy a “full resurrection” in marketing, according to Twitter investor and best-selling author Tim Ferriss. “E-mail addresses are a safer long-term investment than social media features. … Among 20- to 35-year olds, at least, their physical addresses change more frequently than their e-mail addresses,” Ferris said.

• Google’s next big attempt at social media will be a big failure, Likeable Media predicted.

• Retail brands will increasingly combine the power of discounts with the power of social shopping by offering special promotions through platforms such as Facebook and Foursquare, according to MSLGroup.

• As opposed to the current retweet and favorite functions, Twitter will add a “like” button or another lighter-weight way to approve of tweets, according to Likeable Media.

• “Growing mistrust”—particularly about privacy—will make it more difficult for marketers to gather “friends” and followers through social media programs, according to Forrester.

• A group of “disruptive” technologies—cloud, mobile devices and apps, broadband connectivity, social networking and analytics—will move beyond “early adopter” status to form a “new mainstream” platform for growth in the IT industry and for IT vendors, according to IDC.

• Tumblr will emerge to join WordPress as one of the major blogging platforms, according to Likeable Media.

• Social networkers will realize they’re online friends with too many co-workers and acquaintances, according to MSLGroup. As a result, they may scale back their Facebook friends or turn to social networks that are more private.

• Big-name social networks like Facebook, Twitter and LinkedIn will struggle to balance user experience and privacy with profit-making priorities, according to MSLGroup.

• Facebook’s new messaging product will have a “significant impact” on personal e-mail and will harm Gmail, Yahoo and Hotmail, according to Likeable Media.

• New social spam filters will stop many of companies’ tweets and status updates from reaching consumers, according to Forrester.

• The most successful marketing programs won’t be conducted within Facebook, according to Forrester. “Facebook doesn’t own social media in 2011,” the firm said. Successful marketers will “think outside the Facebox,” Forrester predicted.