Usually I'm downloading older stuff that I can't always find in music stores. There are some old albums where, if I came across the LP in a secondhand shop, I'd buy it right then and there.
I've ripped all of my CDs to mp3 Cd for convenience: (
http://www.iriver.com/product/info.asp?p_name=iMP-350)
If I can find a place that sells cheap vinyl, I'll rip and burn that too.
There's only a handful of artists I'd buy new retail price CDs for anyway.