For sometime I was unable to open a magnet-link on Chromium and start downloading it from Deluge. There is a fix for this, the problem is xdg-open. As root, open /usr/bin/xdg-open.

Find the line open_xfce() and replace (or comment) with the following function;

open_xfce() {
   if (echo "$1" | grep -q '^magnet:'); then
      deluge "$1"
   else
      exo-open "$1"
   fi

   if [ $? -eq 0 ]; then
      exit_success
   else
      exit_failure_operation_failed
   fi
}

You can replace deluge with whatever BitTorrent client you’d like, say transmission. I’ve tested this on a Gentoo and in Arch Linux, hopefully this might help on whatever distro you are using.