I listen to music via Spotify every single day. I always listen to music when I walk, I walk about 1 hour every single day, and I always listen to music when I write, I write for at least two hours every single day. I use Spotify to listen to all my music.
I wanted to like Spotify, but last I checked, their selection of Japanese pop music was really limited. Same with Pandora, so I've been using Last.fm and Shoutcast radio stations whenever I want to listen to J-pop, but want something different than the songs I already know.
Also, for those who like Spotify, but want an alternative, Grooveshark.com is pretty similar, and I think it might be open to all countries. It also tends to have a wider selection than Spotify, although their labeling of song tracks isn't always the best, it's usually decent.