I still would like to see a different color used for read-only fields, so I don't know if #4 would work in this case. MC11 used a darker shade similar to #4 to denote the fields that could not be edited (making it easier to quickly find certain fields) so I find it a little confusing to now use the same shades to create the grid.
I think the "lines" approach works best, and of all the choices I've seen so far, I like either #1, or the MC11 approach.
dcwebman -- Thanks for posting these. I have no idea how hard it is to create these mockups, but if you're game, perhaps you could make one like #1, but that includes some read-only fields (date created, bitrate, last played, etc.), and has these values shown with the darker color (like in the left column of #1.) If the value is read-only, the grid lines would be the lighter color all the way accross. I think this might work really well since it would still look "clean," yet it would give us both grid lines AND the different read-only color.
I should note once again that whatever we do, it needs to work in other skins as well. I mention this because at the moment, the "clear rating" icon does NOT work in Thunderstorm -- it essentially vanishes when the mouse is on it. I don't use Noire since it's too bright, and doesn't have a "stop" button. I still like Thunderstorm the best.
Larry