More information might (perhaps) be found at OSM wiki (also see talk page).
The planets are licensed under CC-BY-SA 2.0 (older ones) and ODbL 1.0 (newer ones, after Sep/2012).
More information about licensing can be found here

There is now RSS feed available for monitoring new torrents!
(there are third-party instructions on how to setup RSS with rtorrent, or your bittorrent client may have RSS functionality built-in). Or, you might simply want to download latest planet.osm.bz2.torrent. »
Alternatively, as of Feb/2012, smaller PBF format is available: planet.osm.pbf.torrent. »

Bittorrent client which supports webseed is recommended (but should not be required if everything is functioning down here :) Or you may be using tool like Osm2Garmin which integrates this functionality.

Note: planet-120822 will be last planet to be licensed under CC-BY-SA, see here for more details.

You can also download script used to make this torrent and RSS feed (requires bash, wget, fuser, mktorrent) , or you can also browse all the stuff (for alternative torrents, post-process stuff like RSS etc)

Please direct all feedback to mnalis-osmtorrent _AT_
(You can visit this site via both IPv4 and IPv6)