Trendy CDs are having vinyl-style imperfections added, reports the LA Times [free registration required], though as the article points out, it's a very old idea. Most people probably have a favourite example, though mine is a different kind of trick -- the clicking sound, like a scratched record, at the start of Kraftwerk's LP, Radio Activity. In that case, you only got the full effect the first time you played the LP, and it doesn't make sense on CD.