You know, either I'm old or just old-school: I always purchase ... er, well, "acquire" ... the full album of anyone I listen to. I want to hear the entire ouevre, if you will, of an artist, which largely determines whether they're someone I'll continue to listen to.
A catchy tune is all well and good, but if I'm going to plug something into the CD player - or iPod, or whatever - I want to be able to play it and forget about it.
Might also have to do with the fact that I'm really too lazy to make my own playlists. Even back in the day when we referred to them as "mix tapes."
