Found it!

The responsible package was:
sbc-svn_20070608-1_armel.deb

Which I installed to get my stereo bluetooth headset to work. As soon as I installed this package I could not switch on the N810. I had to reconnect it to the charger before I could turn it back on again (after it had shown the "charging" icon).


The package installs the following files:
$ dpkg -L sbc-svn
/.
/usr
/usr/bin
/usr/bin/sbcinfo
/usr/lib
/usr/lib/libsbc.la
/usr/lib/pkgconfig
/usr/lib/pkgconfig/sbc.pc
/usr/lib/libsbc.so.0.0.0
/usr/lib/libsbc.a
/usr/share
/usr/share/doc
/usr/share/doc/sbc-svn
/usr/share/doc/sbc-svn/README
/usr/share/doc/sbc-svn/NEWS.gz
/usr/share/doc/sbc-svn/copyright
/usr/share/doc/sbc-svn/changelog.gz
/usr/share/doc/sbc-svn/changelog.Debian.gz
/usr/share/aclocal
/usr/share/aclocal/sbc.m4
/usr/include
/usr/include/sbc.h
/usr/lib/libsbc.so
/usr/lib/libsbc.so.0

Nothing strange here, must be the installation scripts that screw things up on the N810. I think the package was intended for the N800, since I already installed it there and it did not cause the same problems.

Well at least its not Nokia's fault.