I'm not an Arch user, but yes, we try our best to push changes upstream, and this is what we have done with kernel changes for Sputnik. I believe that the 3.9 kernel is when the touchpad driver was included upstream. There are some backlight issues, which are not exclusive to Dell Ivy Bridge systems but have affect several other vendors, that are still being worked out, and some of the fixes currently available in Ubuntu may be temporary workarounds for the backlight. I don't recall anything else that wouldn't be upstream.
-- Project Sputnik development lead Software Principal Engineer Linux OS Architecture Dell | Client Product Group