A common arguemnet of those that illegally download music is that they are "window shopping" and then will spend the money later.

A recent study has shown those that download music spend nearly twice as much on music as those that don't download.

http://news.bbc.co.uk/1/hi/technology/8337887.stm

My experience is obviously a little different. I'm in a country were I can't listen to music over the radio. I do download the odd song to keep in touch with Music back home. If I like it I do order the music to have the CD itself. If I don't I delete it (no point having it clutter the hard disk if I don't like it)