apt-cyg and .xz archives
Stock apt-cyg has one more problem, besides the one already fixed before. Yesterday I've noticed, that it fails to install new packages in .tar.xz format (before there were only .tar.bz2). The problem is in these lines:
echo "Unpacking..." cat $file | bunzip2 | tar > "/etc/setup/$pkg.lst" xvf - -C /
echo "Unpacking..." tar -xvf $file -C / > "/etc/setup/$pkg.lst"
apt-cyg fixed the right way can be found in this fork on github.