@PopeJo: thank you for this interesting piece of information. So QL share the same problem as OpenArena, except that in OA there isn't yet a global banlist. With such a system, we should be on par in this domain. And who knows, maybe OA can surpass QL in the future in cheating detection?
@grey matter: metabans isn't in opposition to the 7's suggestion to make a certificate system to identify users and limit abuses, the two are complementary.
Metabans can work standalone (meaning that you can manually upload your banlist, and download other admins' banlists), but it can also be totally automated using third-party tools, like B3, and this is by far the main advantage. Plus, it has a field to store reasons (which B3 support natively), and a different table to
watch players instead of punishing them right away.
This is nothing very innovative technologically, but the concept resides in the web interface that allows for easy sharing and subscription to other's banlists. In this sense, I think it's a very nice tool (and great if it works well, it's still in beta as of January 2012).
About your concerns for privacy, the banlists are anyway to be downloaded on your server, the game engines can't just connect directly to metabans to apply bans. Metabans is only to be used to share, not to apply, so you always have a full backup on your server anyway. Secondly, I trust the author Phogue because he seems to know one of the main dev of B3 that I deeply respect, so for now I give him the presumption of innocence and of good intention.
---------------------------
Also, there was a previous discussion one year and a half ago about the very same issue, with some related proposition (in fact there are mines which didn't change). There is also a patch to authenticate users using a GUID with a RSA 2048 bits key, this might be useful to make a stronger certificate system.
http://openarena.ws/board/index.php?topic=3206.75