encyclo - 11:48 pm on Jan 8, 2011 (gmt 0)

I have created a 57x57 pixel apple-touch-icon.png graphic for Mobile Safari visitors, but I am also getting requests for other variants:

apple-touch-icon-precomposed.png
apple-touch-icon-114x114.png
apple-touch-icon-114x114-precomposed.png

Do I need to create these too, and if so what are they for exactly? What's the difference between the precomposed and non-precomposed variants?