The new module-init-tools 3.8 package changes the location of the configuration file: /etc/modprobe.conf is no longer read, instead /etc/modprobe.d/modprobe.conf is used. Files in /etc/modprobe.d without a .conf suffix will be ignored in the future. Please adjust your local configuration files after the update.

URL: http://www.archlinux.org/news/450/