Do you use your own kernel or the installer kernel ?
The Ubuntu kernels uses initrd as default and loads drivers from that.
If you can't use the keyboard it is probably a module that isn't loaded.
I did not use the Ubuntu kernel... I dropped everything from Arch into the partition and deleted everything Ubuntu... was thinking about saving the syslinux folder from Ubuntu, but wasn't sure if it mattered... can I just copy/paste the Ubuntu kernel or will I have to recompile?
Also, for installing, does Ubuntu offer a GUI or do I dd the partition?
This is complicated; to re-enable USB when we come out of Standby on the Smartbook, we need to reload the USB module, and therefore, it actually is a module and not built-in to the kernel.
When you deleted the installer partition and copied over the Plug rootfs, you deleted all the kernel modules.
What you will need to do is compile a kernel from those sources probably with USB and ext4 built-in (since Ubuntu uses modules, we use modules for now). Ubuntu puts them in the initrd; but that means using Ubuntu's initrd scripts before the real rootfs is mounted. This is probably not what you want.
Once you get that kernel compile done, you can copy the modules to the rootfs and things should be fine. Just don't let the system suspend with USB built-in...