Steven Thank you for the changes you've made so far. I know that even these seemingly small things may take a lot of your time, but the devil's in the details, so thank you for your hard work.
I have yet another set of ideas for your consideration, so here is round two:
1. Extend the headers over the scrollbar like so
http://i.imgur.com/6xlEA.png, i think it would look cleaner that way.
2. Fix "MainPanelMargin.Left" and right preference in skins - Default value 0 leaves a 1px gap between the window border and the panel, this is very bad on the right side where the scrollbar is (it violates Fitts' Law). This can be fixed by setting -1 margin, but then the panel overlaps the skinned window border (in restored state). So maybe make it look like -1 sans overlapping at 0. (this is more of a bug really)
3. Refresh the icons. My proposal
http://i.imgur.com/5SbuR.png these icons are from
http://p.yusukekamiyamane.com/ with some modifications (grab them
here). The best solution imo would be to let skin creators ship their own icons with skins if they choose to. Also it would be much easier if the icons embedded in the xml file were pngs instead. Maybe the skins could be in a zip file with a different extension (like .mbs - musicbee skin) so the skin could be applied by opening the file. In this zip file there would be both the plain xml skin and the bitmap xmlc skin + Icon folder with custom icons.
4. The new arrow expanders are a nice touch, you could apply them to parent nodes in navigator panel and in podcast (and other places if i missed sth) for the sake of consistency.
5. Add a second color for ArtistSplitterLine for a indent effect.
http://i.imgur.com/TYwL0.png6. In the Albums & Tracks view make the rows fade in (as a preference in skin settings, not everybody will like that)
http://i.imgur.com/TYwL0.png7. I would also like you to reconsider the Auto DJ toggle icon. It's not obvious that it is a trigger for sth, there is no tooltip for it or a mouseover effect to indicate that it's a button. Also the panel would look cleaner without it. I'm sure you can come up with a better place for it. I would suggest to incorporate it in the shuffle button, so like the repeat button it has 3 states - off/shuffle/AutoDJ.
I want to make it clear that these are only ideas I would like you to think about and discuss. I know that MusicBee is pretty customizable and there are other people who may use it in different ways that I didn't take into account, and the last thing I want is to make someone's experience worse.