Updating Intel microcode
# pacman -S microcode_ctl
Then add microcode to the DAEMONS array in Template:Filename.
You may have to replace /etc/microcode.dat with a newer version from the intel site, as of December 5th, 2010, the Arch package has an out of date microcode file.
Note: Microcode updates via software are not persistent - they have to be done at each boot (that's the daemon's purpose) - BIOS updates with the new microcode are a cleaner solution but aren't always available