It seems like google has just renamed their SWX (old OpenOffice format) to .odt. This seems very strange.

See http://odf-converter.sourceforge.net/blog/index.php?2006/11/03/14-what-s-the-problem-with-google-docs
for more info.

Well they do call it "Save as OpenOffice" and the file formats are very similar. Hmm...