I used the MusicBrainz API a while back for a side project that got me sued for some reason (http://tcrn.ch/2rEox3h).
As I recall, it was pleasant to work with and did what I needed it to quite nicely, aside from a feature that my code had depended on being removed — anonymous/unauthenticated search — at which point the project was already basically dead and not worth trying to fix (that was just the last nail in the coffin). In any case, nice to see that it's still active.
Unauthenticated search is still possible and allowed, just as long as you use a proper User Agent string. See https://musicbrainz.org/doc/Development/XML_Web_Service/Vers... "Do I need an API key?" and "Do I need to provide authentication?" (In fact, I don't think there is a way to do authenticated searches.)
Well, I hadn't exactly predicted it — the quoted joke was from the top of the site's FAQ page, meant to imply that users of the service would get in trouble for being complicit in copyright infringement / piracy — but it also wasn't all that surprising when it happened. I was sued by the current Napster (https://en.wikipedia.org/wiki/Napster_(streaming_music_servi...) for alleged trademark infringement.
In the end we settled before it ever went to trial, so unfortunately that quote never found its way into a court transcript.
As I recall, it was pleasant to work with and did what I needed it to quite nicely, aside from a feature that my code had depended on being removed — anonymous/unauthenticated search — at which point the project was already basically dead and not worth trying to fix (that was just the last nail in the coffin). In any case, nice to see that it's still active.