When I got my 40gb 4G iPod back in October 2004, I ripped my 500+ cd collection and put it all on my iPod. I have been buying cds since the format came out in the mid 1980's and thought it was great to have my entire music collection in the palm of my hand. I imagined that I would be satisfied with having all that music in my pocket, accessable at the touch of a finger.
Then I discovered the ease with which I could add new music from iTunes and started buying more stuff -- and THEN I discovered allofmp3 and really got started. I snatched up all those wonderful classic rock anthologies that I had never been able to afford, and complete sets of symphonies/concertos/sonatas by Beethoven, Bach, Mozart, etc., etc.
Of course I soon ran out of room on my 40gb iPod and learned how to uncheck some of my music to make room for new stuff. Like Dragfree, I had to admit that 3 versions of Bach's Sonata for Unacompanied Cello might be more than I needed
ITunes makes that very easy, and now I have a lot more music on my computer than I carry on my iPod. Every time I acquire some new recordings I have to make the tough choice of what I will move off to make room for it. But the nice thing is that it isn't gone, it is waiting there in my library for me to listen to it from the cdomputer, or rotate it back to the iPod to be enjoyed again.
So my answer is yes, my iPod did prompt me to buy more music. More than that, it let me enjoy lots of older recordings that I had not listened to for a long time. It encouraged me to look at a lot of new music that I had not heard before and have really enjoyed.
So I think the iPod is the greatest invention since the Victrola. I have tons of great music in the palm of my hand and I enjoy it almost constantly. Well OK, I do unplug and talk to my wife over dinner, but she is the exception.
Just for the record, I have 60.2gb of music in my library of which 23gb is Classical, 18gb is rock/pop, 10gb is jazz. and the rest an eclectic stew. What actually fits on a 40gb iPod is about 37gb of the stuff that made the cut.