Thanks for the feedback!
I should probably make clear that I'm not really a front-end developer or a designer. I've added a few things to fit my personal needs (the new icons, the new album view) but I don't enjoy delving into that. So if you want new icons, or a better layout in general, I'm open for it but I'd need input. Either plain HTML (mine is horrible), new icon packs from someone who knows how to create that, or new code (fork+push at Github) that achieves it. Otherwise it tends to end up pretty far down on my list. But if you mod my code and I like it, I'll gladly put it into my code base.
The top 20 should definitely be configurable and most of all, it needs paging. I'll add that sooner or later (it works on the back-end, just needs GUI).
Also, it's a good idea to extend the left frame. You know how Subsonic adds a drop down menu for multiple media folders? I imagine adding a second drop down menu just like that, with all genres. That would limit the left frame to only show artists matching that. Maybe it's not exactly what you meant but thanks for that idea!
The tracks for the radio are chosen by random among the top 50 most played, fetched from last.fm. The higher the rank a track has, the more likely it is to be picked for the radio, plus that songs you've played a lot yourself and scrobbled to last.fm are favored. The same goes for related artists radio. That means intros, remixes and stuff might be chosen if they've been played a lot by other people. Or if you only have those tracks from an artist and nothing better, MusicCabinet might pick it just to get something. It would be good to allow the track picking algorithm to be more configurable as well, I'll do that some day too. So much code to write, so less time!