While many of the features of MacOS 9.2.1 are hard to see, this one caught my eye as I put my TiBook to sleep after updating it. The sleep light now pulses at least twice as fast and the light-dark cycle is more pronounced (MUCH darker dark… no half-on to bright cycling).

I double checked it by shooting video of a 9.1 and 9.2.1 PB G4 side-by-side and then installing 9.2.1 on that and getting the same results. I made a video of the two in 2x speed and real-time.