I wish I would have taken pictures when I recently rebuilt my system. The old one looked much like Jay's picture, but probably worse. Living out in the sticks and on a road that has a lot of farmland makes it dusty around here, and having a cat doesn't make it any better.
Though I replaced the motherboard, CPU, PSU and memory, I reused everything else, including the case. This time, though, I added filter material to the intakes. I cut the material to size and used double sided tape to hold it in place. It's kind of ugly, but it keeps everything nice and clean. :)