From my experience in running Debian on ARM, I can say that the software difference is really non-existence. Any of the normal Debian OSS software works fine.. I did not run into any problems with software not working except for the closed source programs that didn't have ARM packages. I really can't imagine the architecture shift being that big of a problem, as I'm assuming the bulk of the work for ARM with Debian was just recompiling packages.. I had a working XFCE desktop with common packages like Iceweasel (Firefox), OpenOffice.org, GIMP, and so on that was just as easy to set up as x86.