I recently had issues with a failed USB flash drive and subsequently reinstalled Arch Linux ARM from scratch, on a brand new flash drive. The default installation wasn't enabling networking and I eventually discovered the issue: dhcpcd wasn't enabled by default, so I had to manually enable it. Once I rebooted, I was able to ping the device and connect via ssh.
Another issue is that system locales weren't being generated automatically. I had to manually generate locales, something I'd never done in the past. This may have been a result of the issue with dhcpcd, but I'm not sure.