It's funny how at the beginning of the thread, we're talking about CDs and then it mutates into talking about digital files.
When I first started buying CDs, I kept them alphabetized by artist. When I got to around 100, I got tired of shifting everything around every time I bought a new CD...especially if it was early in the alphabet. At the time, I had a CD rack with slots so I wasn't able to just slide everything over...I had to move each one individually. PITA. So since then I've organized by genre. I group artists and order them chronologically within the artist group. This used to be easier...but over the past decade or so has gotten more confusing for two reasons: 1) I've run out of room and my CD book case is doubled-up...Every shelf has nearly 2 full rows in front of 2 back rows; 2) there is much more genre cross-pollination than there used to be, and I struggle to classify things. It's honestly been kind of a big mess for the past 5 years, but without buying an extra bookcase, it's pointless trying to fix it. And when I get new CDs, they get ripped to my computer right away anyway. It's only a pain when I want to hear an oldie that happens to not be on my computer, and I have to dig it out of the mess. I usually have a good idea of approximately where it is, but often have to dig it out from behind others.