I just set up subsonic a few days ago and noticed the default web-interface was missing similar artists feature, so I spent a few hours and implemented one in javascript. Why Javascript you ask? Because, then we don´t need to recompile subsonic, I think..
Anyway, here is the package: https://github.com/mqchen/SimilarArtist ... r-Subsonic
(Please note that it is only intended as a temporary solution until the feature is implemented in subsonic properly)
It´s not pretty, but it works and looks like this:
It uses MusicBrainz to get the artist´s actual name (incase it is slightly misspelt) and then gets up to 30 similar artists from Last.fm.
In case any one is interested (why javascript and php?). Well, I fist tried a pure Javascript implementation using YQL as a jsonp proxy for MusicBrainz and Last.fm (since they don´t have an jsonp API), but there was a bug, which caused Yahoo to block my IP for YQL (as far as I can tell), so with no luck finding a good jsonp proxy, I just decided to go with php.
If you have any problems just let me know and I´ll try to help!