I've installed Arch and am getting on fine with it - this question is more for the sake of curiosity and my education!
The first time I install the image on to an SD card and run pacman (-Su), the download happens OK, but I get told that there are conflicts with the files "pci.ids" and "usb.ids". On renaming / deleting these files everything runs fine. Running pacman -Qo on the files reveals that pciutils and usbutils packages own these files (unsurprisingly!).
I assume that these files contain information to convert PCI/USB vendor and device id's in to actual functions for loading drivers. The presence of the first file particularly surprised me because AFAIK, RPi does not have PCI. Renaming the files (adding .bak) does not appear to have affected USB device detection or general system stability.
Does anyone know why the files are there, why I get the "file already exists in filesystem" message (rather than pacman just overwriting the files) and why pciutils would be present on the version of ArchLinux available from the RPi download page?