If the rumors are correct, this might explain why Facebook and Google have been going at it recently with concerns to user data--Google has been preventing Facebook from importing Gmail data, and perhaps this is because such a feature would help people migrate from Gmail to Facebook email with ease.
Is Google right to be worried? We won't know for sure until Monday, but, in the meantime, here are five ways Facebook email could keep Gmail on its toes:
Gmail is still behind when it comes to photo integration--sending users to external Websites to view albums in Picasa or Flickr. Even if Facebook ignores these services in email, it will still have its own (immensely popular) photo service to rely on. A slideshow viewer directly in Facebook email, like Yahoo's Picasa and Flickr viewer, could be a killer feature.
Smarter Conversation View
Google satisfied the anti-thread contingent in September when it allowed Gmail users to disable conversation view. But maybe these people wouldn't have had so much rage if Gmail were simply better at threading conversations. Facebook already does a decent job threading status updates, displaying the first message in full, followed by recent comments. A similar system will work nicely for email.
Ever get an email from someone, but can't remember exactly who it is? I'd love to see Facebook tie-in profile data from the people you're friends with, or whose information is public. This could include photo thumbnails and details that normally appear on the "info" tab on profile pages. Actually, an "info" tab on emails would be great.
I'm still not completely sold on Facebook Groups, which are supposed to be an organic way of organizing contacts by association. But the idea might be more alluring if it were carried over to email. An automatic labeling system for group e-mail blasts could allow users to see the messages they want and ignore the ones they don't.
The "Like" in Links
The "Like" button is the most popular new feature Facebook has introduced in recent memory. In just a few months, it's gotten all over the Web. Why not extend it to e-mail? Whenever someone sends a link in the rumored Facebook mail, it'd be nice to see how many other friends have already checked it out, and what they've said about it in their news feeds.