Did install Kde4 the other day and looking at what was going to be uninstalled I looked for some way to get my box up and running again if things went south.

What did work (almost) perfect was:

dpkg --get-selections > /etc/package.selections # save the list of installed packages

To save a the current installed package list.Once everything is screwed up reinstall with:

dpkg --set-selections < /etc/package.selections && apt-get dselect-upgrade

It might not work perfect depending on how bad a mess it is (switching repositories between stable/testing/sid and experimental and funny stuff like that) but after a few additonal apt-gets and aptitude to clean up the final mess things tend to work again as before.

Note:I didn't come up with this.Just thought I share it.

For those who want to test kde4 in parallel with another window manager, you can do it in a chroot:

http://wiki.debian.org/Kde4schroot

kda4 was working fine - the little problem was just that I didn't have the time or energy available to migrate everybodys settings for email and the likes and no - copy from ./kde3.x/share/apps didn't work for me.