I tried to use the default magic.mime file on /usr/share and I got few problems like seg faults and incorrect mimetypes, specially from m$-office.
The workaround for this problem is use the default magic file for the apache installation (for who uses the apache). This file is set by default in ServerRoot/conf/magic.
Then you should set (or reset) the directive mime_magic.magicfile = "/etc/httpd/conf/magic" (change the obsolute path to yours...) in php.ini file.
Restart the web server, take a look on phpinfo() functions to check if all changes were made and enjoy it.
Remember to compile php with option --enable-mime-magic (version <= 4.3.1) or --with-mime-magic (version >= 4.3.2)