I JUST finished gluing this together. Its the most recent release version of Transmission (2.33), tweaked and tuned to run fairly well on the Javelin. Install the plugin and visit port 9091 on your Javelin (for example http://s4:9091). The username is 'transmission' and the password is 'password'
By default everything goes in the /VOLUME1/DOWNLOADS folder. if this is not correct, edit the settings (click lower left corner gear icon and click preferences).
1) Disabling the plugin is not possible via web interface. Just login to telnet and issue '/APP/TRANSMISSION/bin/transmission_control stop'
2) Package is fairly large, possibly larger than it has to be. I will see if there is something I can do to manage the bloat. Right now it is at 17MB.
It seems to download fairly happily at 3MB/s (about 25mbit/s) from a well seeded file using 75% or so of the CPU. That is with encrypted clients.