Currently we have several of what I'll call "advisory rate-limits" – e.g. http://stats.musicbrainz.org/mrtg/drraw/drraw.cgi?Mode=view;Template=1262469754.29207;Base=%2Fvar%2Fwww%2Fmrtg%2F%2Flenny_ratelimit-default-picard-rate.rrd for picard. python-musicbrainz-ngs would be a nice one to add, especially since headphones is using it nowadays, and they're back to 33% of our traffic with it (and another 14% with the old UA string): http://stats.musicbrainz.org/webstats/zaphod/musicbrainz-full/usage_201207.html#TOPAGENTS

python-musicbrainz-ngs has a UA string of the format: "<specific usage details> python-musicbrainz-ngs/<version> ( <url/email for the library using pymbngs> )" or "<specific usage details python/musicbrainz-ngs/<version>" (the latter when no contact info is provided).

Other client libraries may also fit into this category, e.g. libmusicbrainz4/5 (with UA format "<details> libmusicbrainz

/<version> <neon version details>").

Just a wishlist item for me, but it could be useful!