Facebook’s newly announced messaging platform will deeply integrateMicrosoft’s Office Web Apps so that Facebook users can view Word, Excel and PowerPoint attachments without having to leave the site. Rumors about this integration started to make the rounds on the Internet last week. Oddly, though, Facebook didn’t mention this integration during today’s press conference and makes no mention of it in the official announcement on its corporate blog.

As Takeshi Numoto, Microsoft’s corporate VP of the Office Product Management group, notes, this new integration will allow Facebook users to share “ideas and documents – serious or entertaining.” Microsoft envisions that Facebook users will use this integration to send personalized dinner party invitations to their Facebook friends with the help of Word, and that your kids will use it to share that PowerPoint presentations they created for their last school project. While Microsoft points out that this integration can also be used for “serious” business, business users aren’t likely to share their documents through the Facebook platform, after all.

For Microsoft, this is a major win, as its flagship Web productivity apps will now play a central role on the Web’s most popular social network. Microsoft already integrated Facebook into Bing last month and the Office Web apps were among the first service to use Facebook’s Instant Personalization feature.