Before I got my iPhone, foobar2000 was my primary music player. Which feature do I miss most after making the switch to iTunes? Not the lightweight-ness, not the components (add-ons), but the ability to control the player using hotkeys no matter what you are doing on your PC.
Say I want to watch a YouTube video. I would have to summon the iTunes window just to pause the song, then switch back to my web browser to play the video. If I were using foobar2000, I would just need to hit the hotkey to pause the song while I’m still on my web browser, making things faster and less tedious.