Brian Jones, Program Manager for MS Word team announced the new file formats in the next Office System a.k.a Office 12.
According to him, most of the file extensions are also going to be suffixed by "X" (DOCX, PPTX, XLSX etc...)
For security reasons the Macro-Enabled file types in Office System will be treated as different file types (.xlsm) in Office 12.Excerpt from Brian's Blog
Since Office 12 is going to take us in to pure native world of XML, Horizons are almost touching sky for Developement. Certainly this is a great news for Developer Community. Office 12 is going to give ability to developers to examine the contents of the file with out writing a single line of code. They can treat these files just like any other zip file.
Download this Document which talks about the New Office XML format and Preview for Developers.
Channel 9 featured a very interesting demo of the same here