A small feedback from my side. I followed this link
to compile rtorrent 0.8.9 - the first version with a support for magnets. I compiled on Slackware 13.1. Everything went fine. Of course I didn't follow Debian related issues. SImply downloaded and ran the the provided build script for rtorrent.
I have a small installation issues - cause now I have two different versions of rtorrent. Note that the script doesn't really install rtorrent system-wide. It simply creates ~/bin ~/lib directories and places there all executable and libraries. So you can run the script as a common user.
For interested - the sources provide some enhancements - like coloring and many others. I am not really interested cause I always run "screen rtorrent" - to push rtorrent into background.