I am currently downloading the actual ubuntu-distro with 1400 KB/s along with to other small test torrents to make sure it really works. And it does.
After all it can be said the solution to the crash issue was almost too simple:
Responsible for rtorrents crash behaviour was the oom-killer (cf. earlier posts) that is shipped with debian etch.
However, uprading to lenny solves this issue.
That can be done by simply typing:
apt-get update
apt-get dist-upgrade
Before Upgrading, make sure you have a backup at hand:
sudo cat /dev/mtdblock* > backup.img...and store it to a safe location. With this precaution you can always switch back to a working system by putting the NSLU2 into upgrade mode and flashing the backup.img to it with upslug2.
The upgrade may take a considerable time.
Note that I crashed my Debian NSLU2 by doing this because the "new initramfs-tools in testing (version 0.92) generates a ramdisk that does not boot correctly on the NSLU2 - it makes your system unbootable (see bug #478236)."
As mentioned, the upgrade is currently not safe.
As I crashed my NSLU2 and had no backups but also no important data on it, I snapped at the chance and reinstalled my system with the debian 5.0 beta 1 (unoffical), see here.
If you have any questions, leave a comment!
UPDATE July 28: Upgrading via apt-get dist-upgrade should be safe now.
