The new mkinitcpio 0.6 brings lots of changes, most importantly the removal of klibc in favor of glibc and busybox. This update should be flawless and completely invisible to the end user, but if you are paranoid you can still backup your old initramfs image and regenerate it directly after the update to be sure.
If you use a root filesystem on NFS, you need to install the new package mkinitcpio-nfs-utils.
If you are interested, you can find more details about the changes on my blog.