Changing the desktop default after installing Debian without giving it a second thought is a pain if one is not very familiar with debconf (a.k.a., the spawn from hell, second only to Solaris’ SMF oh, how I loath thee —until I get close to some iron with AIX inside anyways.) You love The Debian Way(tm), and you strive to always use it despite all odds. And what odds! There is no easy and obvious way to change the default desktop in a Debian system, just the following:
echo "tasksel tasksel/desktop string xfce" | debconf-set-selections
 Yes, I’m bitching too much, but how do you expect a luser to do this without suffering a heart attack? Wait I use Debian, not Ubuntu. Thank you $DEITY!