Exported a WXR file from a blog and tried to import it on a new install of wpmu but get the following error:
Warning: Invalid argument supplied for foreach() in /home/my-path/wp-admin/import/wordpress.php on line 117
Also, even if I mapped to an existing user (admin) it created a new user with all fields blank.
The result was that it DID actually map posts to the selected user but it imported all posts but without a title.