My experience with Song has been like my experience with the new 757-200s with the Satellite TVs (heck, these were the same planes). Only real difference is that food was buy-on-board (not a big fan of that, I normally grab something in the terminal). Not a whole lot of difference between mainline and Song for me; I'm glad DL did learn some things from it (keeping the PTVs, reduced turn times at stations, etc.).