I used Jinzora for a few weeks, while I don't like the application very much, I can say it did have one interesting feature; download profiles.
Just as users on the web interface can create and define "Players" with different transcoding and bitrate options, I would like to have a similar function but for "Download Profiles". As the core transcoding is already a part of Subsonic, I think this would technically be not too far out of line to request as a feature.
This would entail a user being able to create a download profile, specifying which file format they want an input file converted to, and what bitrate. Of course, they may want to download the raw un-transcoded file in the native file format it is on the server, and that too should be an option, as it already is.
The idea though is, that I could have my entire .FLAC collection on my server, and download and have Subsonic transcode on the fly for me, the songs to .mp3 format for easy use on my iPod or with my Pioneer AVH-P4100DVD in car head unit.
If you have any questions or need further clarification on my suggestion, please ask.