Quick post here, as most of the activity is now on SfE Forum (see previous post for link). I just tested SfE on Office 2011 for Mac.
Works reasonably well but needs some modifications (shadow is added by default and other display weird things). No Ribbon however and I also have to find a way to make a proper menu with all formulas.
I got my hands on Office 2013 x64(sleek interface ;-) I like it so far) and got SfE working there too... good news ! There is a good chance that you can create an SfE *.xls in Office 2003 (almost previous century software guys !)and still use it in Office 2013.
See SfE running running on both environments :