I never noticed this until just this morning.
I was listening to my iPhone and a Nine Inch Nails song came on (Lights in the Sky), and I went to rate it... when I noticed there were lyrics on the screen. At first I thought it was my album art, but I had never seen this before, so I tapped the screen to confirm whether they were generated by iTunes... and lo and behold, they were. Scrollable too.
Anyone know what I need to enable with my album art to support this? I have thousands and thousands of MP3s, but I've never seen this particular feature.