I'm running Subsonic on a model B 512MB (on Wheezy, and Java 8 hard-float) for 2 months now, and it works just great, including the jukebox mode. (I just have to get a audio mixer for my amp, so I can seamlessly switch from listening from my android device to my home amp.)
Performance is fine, only the first boot is horribly slow (does it update its library then?). I got a 2TB (only 150GB of music though) external harddrive connected, formatted as NTFS. The NTFS driver in the pi is quite CPU intensive and indexing is slow, but I want to be able to use the hdd with my windows PC too... Also I use the rPi as samba fileserver for backups, and It works well. It also manages to run XBMC alongside, but the interface is too slow anyway for my taste.
I don't use Subsonic for video, so I can't comment on that.
I got 2 minor issues with the setup though:
- last.fm scrobbling doesn't work
- the HDD won't spin down after usage, and gets quite hot. But that may be a linux problem with this disk.
EDIT:
Both issues have been fixed. I used the wrong last.fm username... Stupid me. but got no warning. The HDD spins down correctly now, but with Deluge as torrent client it's rarely idle...