Since Retro ROMS seems to have fallen off the web lately, I haven’t had anywhere to keep up with my MAME ROMs. The other came I came across The Pleasure Dome (pretty suss sounding name if you ask me). They, along with Petr1fied’s Tracker host some bittorrents for keeping up to date with all your ROMs. Bittorrent comes in handy, since instead of having to run ClrMamePro to figure out what you’re missing (although running it does help clean up unrequired ROMs) and then download each ROM one by one, Bittorrent along with TorrentZip can do all the hard work for you.
Basically you run TorrentZip on your ROMs directory. It re-zips all your ROMs to match the hash for all the ROMs in the bittorrent. It’ll take a few hours to do this if you’ve got stacks of ROMs. After you’ve done that, its a matter of joining the torrent, pointing your bittorrent client at your ROMs directory and away you go. I joined in the torrent the other day at around 67%. Looks like my collection was a tad out of date :-\
For more indepth instructions, check out the guides on how to do it over at the Pleasure Dome.